net: Move call_fib_rule_notifiers up in fib_nl_newrule

Move call_fib_rule_notifiers up in fib_nl_newrule to the point right
before the rule is inserted into the list. At this point there are no
more failure paths within the core rule code, so if the notifier
does not fail then the rule will be inserted into the list.

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>