[INET]: Small possible memory leak in FIB rules

This patch fixes a small memory leak. Default fib rules can be deleted by
the user if the rule does not carry FIB_RULE_PERMANENT flag, f.e. by
	ip rule flush

Such a rule will not be freed as the ref-counter has 2 on start and becomes
clearly unreachable after removal.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>