fib: remove a useless synchronize_rcu() call

fib_nl_delrule() calls synchronize_rcu() for no apparent reason,
while rtnl is held.

I suspect it was done to avoid an atomic_inc_not_zero() in
fib_rules_lookup(), which commit 7fa7cb71 added anyway.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/fib_rules.c

@@ -494,7 +494,6 @@ static int fib_nl_delrule(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
 			}
 		}
 
-		synchronize_rcu();
 		notify_rule_change(RTM_DELRULE, rule, ops, nlh,
 				   NETLINK_CB(skb).pid);
 		fib_rule_put(rule);