ip6mr: delete redundant judgment statements

The initial value of err is -ENOBUFS, and err is guaranteed to be
less than 0 before all goto errout. Therefore, on the error path
of errout, there is no need to repeatedly judge that err is less than 0,
and delete redundant judgments to make the code more concise.
Signed-off-by: Li Zetao <lizetao1@huawei.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6mr.c

@@ -2431,7 +2431,6 @@ static void mr6_netlink_event(struct mr_table *mrt, struct mfc6_cache *mfc,
 
 errout:
 	kfree_skb(skb);
-	if (err < 0)
 	rtnl_set_sk_err(net, RTNLGRP_IPV6_MROUTE, err);
 }