IP: Cleanups

Use symbols instead of magic constants while checking PMTU discovery
setsockopt.

Remove redundant test in ip_rt_frag_needed() (done by caller).

Signed-off-by: John Dykstra <john.dykstra1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index c602d98..2445fed 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -575,7 +575,7 @@
 		inet->hdrincl = val ? 1 : 0;
 		break;
 	case IP_MTU_DISCOVER:
-		if (val < 0 || val > 3)
+		if (val < IP_PMTUDISC_DONT || val > IP_PMTUDISC_PROBE)
 			goto e_inval;
 		inet->pmtudisc = val;
 		break;