Always create loopback routes on every fib

Always create loopback routes on every fib

Always create loopback routes on every fib, for both IPv4 and IPv6

etc/rc.d/routing
	Create loopback IPv4 and IPv6 routes on every fib at boot. Revert
	278302; now that all FIBs have IPv6 loopback routes, the
	"route add -reject" commands won't fail.

tests/etc/rc.d/routing_test.sh
	Greatly simplify static_ipv6_loopback_route_for_each_fib. It was
	written under the assumption that loopback routes would be added to
	a given fib by the kernel as soon as an interface is configured on
	that fib. However, the logic can be much simpler now that we simply
	add loopback routes to all fibs at boot. This also removes the need
	to run the test as root, removes the restriction that
	net.add_addr_allfibs=0, and removes the need to configure fibs in
	kyua.conf.

	Also, add a test case for IPv4 loopback routes

Sponsored by:	Spectra Logic Corp
Differential Revision:	https://reviews.freebsd.org/D6582