net: Simplify GRE case in flow_dissector

Do break when we see routing flag or a non-zero version number in GRE
header.
Acked-by: NJiri Pirko <jiri@resnulli.us>
Signed-off-by: NTom Herbert <tom@herbertland.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/flow_dissector.c

@@ -308,7 +308,9 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		 * Only look inside GRE if version zero and no
 		 * routing
 		 */
-		if (!(hdr->flags & (GRE_VERSION|GRE_ROUTING))) {
+		if (hdr->flags & (GRE_VERSION | GRE_ROUTING))
+			break;
+
 		proto = hdr->proto;
 		nhoff += 4;
 		if (hdr->flags & GRE_CSUM)
@@ -331,8 +333,6 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 		}
 		goto again;
 	}
-		break;
-	}
 	case IPPROTO_IPIP:
 		proto = htons(ETH_P_IP);
 		goto ip;