Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Make test scripts under tests/... non-executable

Executable bits should be set at install time instead of in the repo.
Setting executable bits on files triggers false positives with Phabricator.

MFC after: 2 months

Check if IPv6 supported before running the test, skip otherwise.

Sponsored by: DARPA, AFRL
Sponsored by: HEIF5

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

Move all test integration pieces for etc/ from etc/ to tests/

This is being done to fix breakage with make distribution with read-only
source trees as make distribution doesn't use make obj like building
tests/ does in all cases

Reported by: Wolfgang Zenker <wolfgang@lyxys.ka.sub.org>
Suggested by: jhb
X-MFC with: r282059
MFC after: 1 week