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.c b/net/rarp.c
index 660a02c..bd073c3 100644
--- a/net/rarp.c
+++ b/net/rarp.c
@@ -41,7 +41,7 @@
 /*
  *	Handle a RARP received packet.
  */
-void rarp_receive(IP_t *ip, unsigned len)
+void rarp_receive(struct ip_udp_hdr *ip, unsigned len)
 {
 	ARP_t *arp;