netinet tests: basic VRRP tests

Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D44775

Remove $FreeBSD$: one-line sh pattern

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

carp test: improve jail names for unicast_ll_v6 test

Rename the jails used in the unicast_ll_v6 test, to ensure the jail
names are unique to this test.
That is one of the requirements for running these tests in parallel.

carp tests: test unicast carp via link-local addresses

Sponsored by: Rubicon Communications, LLC ("Netgate")

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

carp tests: unicast tests (IPv6)

Test the new unicast carp mode for IPv6.

There's a routing hop between the peers, to ensure that the TTL check is
correctly disabled for unicast carp.

Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D38942

carp tests: unicast tests (IPv4)

Test the new unicast carp mode for IPv4.

There's a routing hop between the peers, to ensure that the TTL check is
correctly disabled for unicast carp.

Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D38941

carp tests: test manually switch between backup and master

There's been at least one issue where we failed to correctly enter
NET_EPOCH that was triggered in this scenario.
Add a test case for it to make it easier to detect issues like this in
the future.

Reviewed by: zlei
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D39115

carp tests: ensure exactly one jail is master

Verify that we only have one master, not two.

Sponsored by: Rubicon Communications, LLC ("Netgate")

tests/netinet: add test for IPv6 NS and CARP

PR: 193280
Reviewed by: melifaro
Differential revision: https://reviews.freebsd.org/D33859

carp tests: negative demotion

PR: 259528
Reviewed by: donner
MFC after: 3 weeks
Sponsored by: Modirum MDPay
Differential Revision: https://reviews.freebsd.org/D32760

ping: fix some man pages and tests after r368045

MFC-with: r368045

carp tests: Basic functionality test

Set up three vnet jails, bridged together. Run carp between two of them.
Attempt to provoke locking / epoch issues.

Reviewed by: mav (previous version), melifaro, asomers
Differential Revision: https://reviews.freebsd.org/D24303