net: cosmetic: Un-typedef IP_t

Rename IP header related things to IP_UDP. The existing definition
of IP_t includes UDP header, so name it to accurately describe the
structure.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/net/rarp.h b/net/rarp.h
index fc5b363..ebd748e 100644
--- a/net/rarp.h
+++ b/net/rarp.h
@@ -36,7 +36,7 @@
 extern int RarpTry;
 
 /* Process the receipt of a RARP packet */
-extern void rarp_receive(IP_t *ip, unsigned len);
+extern void rarp_receive(struct ip_udp_hdr *ip, unsigned len);
 extern void RarpRequest(void);	/* Send a RARP request */
 
 /**********************************************************************/