ipv4: route: fix drop reason being overridden in ip_route_input_slow

When jumping to 'martian_destination' a drop reason is always set but
that label falls-through the 'e_nobufs' one, overriding the value.

The behavior was introduced by the mentioned commit. The logic went
from,

	goto martian_destination;
	...
  martian_destination:
	...
  e_inval:
	err = -EINVAL;
	goto out;
  e_nobufs:
	err = -ENOBUFS;
	goto out;

to,

	reason = ...;
	goto martian_destination;
	...
  martian_destination:
	...
  e_nobufs:
	reason = SKB_DROP_REASON_NOMEM;
	goto out;

A 'goto out' is clearly missing now after 'martian_destination' to avoid
overriding the drop reason.

Fixes: 5b92112 ("net: ip: make ip_route_input_slow() return drop reasons")
Reported-by: Sabrina Dubroca <[email protected]>
Cc: Menglong Dong <[email protected]>
Signed-off-by: Antoine Tenart <[email protected]>
Reviewed-by: Sabrina Dubroca <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: atenart

net/ipv4/route.c

@@ -2445,6 +2445,7 @@ ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 		net_warn_ratelimited("martian destination %pI4 from %pI4, dev %s\n",
 				     &daddr, &saddr, dev->name);
 #endif
+	goto out;
 
 e_nobufs:
 	reason = SKB_DROP_REASON_NOMEM;