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/tftp.c b/net/tftp.c
index bc7fe05..a04a832 100644
--- a/net/tftp.c
+++ b/net/tftp.c
@@ -322,7 +322,7 @@
 	 *	We will always be sending some sort of packet, so
 	 *	cobble together the packet headers now.
 	 */
-	pkt = (uchar *)(NetTxPacket + NetEthHdrSize() + IP_HDR_SIZE);
+	pkt = NetTxPacket + NetEthHdrSize() + IP_UDP_HDR_SIZE;
 
 	switch (TftpState) {
 	case STATE_SEND_RRQ: