Use the configure check from r21351 and use it to properly define struct

sockaddr (in case it's not missing) so it always works on the system that
we are defining it for, in a RFC-2553/3493-compliant way (i.e. containing
a ss_family field). which is used in udp.c. Patch by Martin Storsjö
<$firstname $firstname st>.

Originally committed as revision 21352 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/network.h

@@ -70,7 +70,15 @@ int inet_aton (const char * str, struct in_addr * add);
 
 #if !HAVE_STRUCT_SOCKADDR_STORAGE
 struct sockaddr_storage {
-    struct sockaddr_in x;
+#if HAVE_STRUCT_SOCKADDR_SA_LEN
+    uint8_t ss_len;
+    uint8_t ss_family;
+#else
+    uint16_t ss_family;
+#endif
+    char ss_pad1[6];
+    int64_t ss_align;
+    char ss_pad2[112];
 };
 #endif