net: cosmetic: Un-typedef ICMP_t

Remove typedef and lower-case name

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/net/ping.c b/net/ping.c
index 04a594c..3102521 100644
--- a/net/ping.c
+++ b/net/ping.c
@@ -100,7 +100,7 @@
 
 void ping_receive(struct ethernet_hdr *et, struct ip_udp_hdr *ip, int len)
 {
-	ICMP_t *icmph = (ICMP_t *)&(ip->udp_src);
+	struct icmp_hdr *icmph = (struct icmp_hdr *)&ip->udp_src;
 	IPaddr_t src_ip;
 
 	switch (icmph->type) {