Include dlfcn.h for RTLD_NOW and friends.

There is a test in sr_module.h which tests whether the macro RTLD_NOW is
defined and defines it to DL_LAZY if not. The header file did not include
dlfcn.h which defines the macro RTLD_NOW, so as a result it was always
re-defined to DL_LAZY.

sr_module.h

@@ -58,6 +58,8 @@
 #ifndef sr_module_h
 #define sr_module_h
 
+#include <dlfcn.h>
+
 #include "parser/msg_parser.h" /* for sip_msg */
 #include "version.h"
 #include "rpc.h"