net: set fib rule refcount after malloc

The configure callback of fib_rules_ops can change the refcnt of a
fib rule. For instance, mlxsw takes a refcnt when adding the processing
of the rule to a work queue. Thus the rule refcnt can not be reset to
to 1 afterwards. Move the refcnt setting to after the allocation.

Fixes: 5361e209 ("net: avoid one splat in fib_nl_delrule()")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>