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/sntp.c b/net/sntp.c
index 69cddb1..07d036d 100644
--- a/net/sntp.c
+++ b/net/sntp.c
@@ -31,7 +31,7 @@
 	pkt.vn = NTP_VERSION;
 	pkt.mode = NTP_MODE_CLIENT;
 
-	memcpy((char *)NetTxPacket + NetEthHdrSize() + IP_HDR_SIZE,
+	memcpy((char *)NetTxPacket + NetEthHdrSize() + IP_UDP_HDR_SIZE,
 		(char *)&pkt, pktlen);
 
 	SntpOurPort = 10000 + (get_timer(0) % 4096);