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/dns.c b/net/dns.c
index 7a3f1f9..cc7ed51 100644
--- a/net/dns.c
+++ b/net/dns.c
@@ -45,7 +45,7 @@
 	enum dns_query_type qtype = DNS_A_RECORD;
 
 	name = NetDNSResolve;
-	pkt = p = (uchar *)(NetTxPacket + NetEthHdrSize() + IP_HDR_SIZE);
+	pkt = p = (uchar *)(NetTxPacket + NetEthHdrSize() + IP_UDP_HDR_SIZE);
 
 	/* Prepare DNS packet header */
 	header           = (struct header *) pkt;