Fix invalid comparison warnings: [-Wbool-compare] and [-Wenum-compare]

Fixes the following GCC 5 warnings and actual bugs:
```
drivers/unix/net_socket_posix.cpp:562:28: warning: comparison between 'enum IP::Type' and 'enum NetSocket::Type' [-Wenum-compare]
modules/gdscript/gdscript_function.cpp:792:26: warning: comparison of constant '17' with boolean expression is always true [-Wbool-compare]
modules/gdscript/gdscript_function.cpp:792:26: warning: logical not is only applied to the left hand side of comparison [-Wlogical-not-parentheses]
modules/gdscript/gdscript_parser.cpp:5082:58: warning: comparison of constant '6' with boolean expression is always false [-Wbool-compare]
modules/gdscript/gdscript_parser.cpp:5082:58: warning: logical not is only applied to the left hand side of comparison [-Wlogical-not-parentheses]
modules/mbedtls/stream_peer_mbed_tls.cpp:286:45: warning: comparison between 'enum StreamPeerTCP::Status' and 'enum StreamPeerSSL::Status' [-Wenum-compare]
modules/mbedtls/stream_peer_mbed_tls.cpp:313:45: warning: comparison between 'enum StreamPeerTCP::Status' and 'enum StreamPeerSSL::Status' [-Wenum-compare]
```

drivers/unix/net_socket_posix.cpp

@@ -559,7 +559,7 @@ void NetSocketPosix::set_ipv6_only_enabled(bool p_enabled) {
 
 void NetSocketPosix::set_tcp_no_delay_enabled(bool p_enabled) {
 	ERR_FAIL_COND(!is_open());
-	ERR_FAIL_COND(_ip_type != TYPE_TCP);
+	ERR_FAIL_COND(!_is_stream); // Not TCP
 
 	int par = p_enabled ? 1 : 0;
 	if (setsockopt(_sock, IPPROTO_TCP, TCP_NODELAY, SOCK_CBUF(&par), sizeof(int)) < 0) {

modules/gdscript/gdscript_function.cpp

@@ -789,7 +789,7 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 #ifdef DEBUG_ENABLED
 				GDScriptNativeClass *nc = Object::cast_to<GDScriptNativeClass>(type->operator Object *());
 				GD_ERR_BREAK(!nc);
-				if (!src->get_type() != Variant::OBJECT && !src->get_type() != Variant::NIL) {
+				if (src->get_type() != Variant::OBJECT && src->get_type() != Variant::NIL) {
 					err_text = "Trying to assign value of type '" + Variant::get_type_name(src->get_type()) +
 							   "' to a variable of type '" + nc->get_name() + "'.";
 					OPCODE_BREAK;

modules/gdscript/gdscript_parser.cpp

@@ -5079,7 +5079,7 @@ void GDScriptParser::_determine_inheritance(ClassNode *p_class) {
 				if (found) continue;
 
 				if (p->constant_expressions.has(base)) {
-					if (!p->constant_expressions[base].expression->type == Node::TYPE_CONSTANT) {
+					if (p->constant_expressions[base].expression->type != Node::TYPE_CONSTANT) {
 						_set_error("Could not resolve constant '" + base + "'.", p_class->line);
 						return;
 					}

modules/mbedtls/stream_peer_mbed_tls.cpp

@@ -29,9 +29,11 @@
 /*************************************************************************/
 
 #include "stream_peer_mbed_tls.h"
+
 #include "core/io/stream_peer_tcp.h"
 #include "core/os/file_access.h"
-#include "mbedtls/platform_util.h"
+
+#include <mbedtls/platform_util.h>
 
 static void my_debug(void *ctx, int level,
 		const char *file, int line,
@@ -283,7 +285,7 @@ void StreamPeerMbedTLS::poll() {
 	}
 
 	Ref<StreamPeerTCP> tcp = base;
-	if (tcp.is_valid() && tcp->get_status() != STATUS_CONNECTED) {
+	if (tcp.is_valid() && tcp->get_status() != StreamPeerTCP::STATUS_CONNECTED) {
 		disconnect_from_stream();
 		return;
 	}
@@ -310,7 +312,7 @@ void StreamPeerMbedTLS::disconnect_from_stream() {
 		return;
 
 	Ref<StreamPeerTCP> tcp = base;
-	if (tcp.is_valid() && tcp->get_status() == STATUS_CONNECTED) {
+	if (tcp.is_valid() && tcp->get_status() == StreamPeerTCP::STATUS_CONNECTED) {
 		// We are still connected on the socket, try to send close notity.
 		mbedtls_ssl_close_notify(&ssl);
 	}

modules/mbedtls/stream_peer_mbed_tls.h

@@ -33,12 +33,12 @@
 
 #include "core/io/stream_peer_ssl.h"
 
-#include "mbedtls/config.h"
-#include "mbedtls/ctr_drbg.h"
-#include "mbedtls/debug.h"
-#include "mbedtls/entropy.h"
-#include "mbedtls/net.h"
-#include "mbedtls/ssl.h"
+#include <mbedtls/config.h>
+#include <mbedtls/ctr_drbg.h>
+#include <mbedtls/debug.h>
+#include <mbedtls/entropy.h>
+#include <mbedtls/net.h>
+#include <mbedtls/ssl.h>
 
 #include <stdio.h>
 #include <stdlib.h>