net: add random_port() prototype

The random_port() is meant to be used by other net code, but without a
prototype, we get fun warnings like:
dns.c: In function 'DnsSend':
dns.c:89: warning: implicit declaration of function 'random_port'

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>

include/net.h

@@ -517,6 +517,9 @@ extern ushort getenv_VLAN(char *);
 /* copy a filename (allow for "..." notation, limit length) */
 extern void	copy_filename (char *dst, char *src, int size);
 
+/* get a random source port */
+extern unsigned int random_port(void);
+
 /**********************************************************************/
 
 #endif /* __NET_H__ */