ipv6 sit: Set relay to 0.0.0.0 directly if relay_prefixlen == 0.

ipv6 sit: Set relay to 0.0.0.0 directly if relay_prefixlen == 0.

Do not use bit-shift if relay_prefixlen == 0;
relay_prefix << 32 does not result in 0.

Signed-off-by: YOSHIFUJI Hideaki <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv6/sit.c

···
 					 ip6rd.prefixlen);
 			if (!ipv6_addr_equal(&prefix, &ip6rd.prefix))
 				goto done;
-			relay_prefix = ip6rd.relay_prefix &
-				       htonl(0xffffffffUL <<
-					     (32 - ip6rd.relay_prefixlen));
+			if (ip6rd.relay_prefixlen)
+				relay_prefix = ip6rd.relay_prefix &
+					       htonl(0xffffffffUL <<
+						     (32 - ip6rd.relay_prefixlen));
+			else
+				relay_prefix = 0;
 			if (relay_prefix != ip6rd.relay_prefix)
 				goto done;