[Net] Fix ENet 'connect_to_host' creating only one channel.

Passing `0` to `enet_host_create` will allow the maximum amount of
channel supported by ENet. For some reasons, `connect_to_host` will
instead only create 1 channel when passed `0`.
This commit normalize the behaviour to always allocate the maximum
allowed channels when passing `0`.

modules/enet/enet_connection.cpp

@@ -107,7 +107,7 @@ Ref<ENetPacketPeer> ENetConnection::connect_to_host(const String &p_address, int
 	address.port = p_port;
 
 	// Initiate connection, allocating enough channels
-	ENetPeer *peer = enet_host_connect(host, &address, p_channels, p_data);
+	ENetPeer *peer = enet_host_connect(host, &address, p_channels > 0 ? p_channels : ENET_PROTOCOL_MAXIMUM_CHANNEL_COUNT, p_data);
 
 	if (peer == nullptr) {
 		return nullptr;