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 7fa7cb7109d07 added anyway.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index 21698f8..1bc3f25 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -494,7 +494,6 @@
 			}
 		}
 
-		synchronize_rcu();
 		notify_rule_change(RTM_DELRULE, rule, ops, nlh,
 				   NETLINK_CB(skb).pid);
 		fib_rule_put(rule);