pf: allow states to be killed by their pre-NAT address

If a connection is NAT-ed we could previously only terminate it by its
ID or the post-NAT IP address. Allow users to specify they want look for
the state by its pre-NAT address. Usage: `pfctl -k nat -k <address>`.

See also: https://redmine.pfsense.org/issues/11556
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D42312

Remove $FreeBSD$: two-line nroff pattern

Remove /^\.\\"\n\.\\"\s*\$FreeBSD\$$\n/

pfctl.8: Use the serial comma

Pointed out by: Pau Amma.
Sponsored by: Rubicon Communications, LLC ("Netgate")

pfctl: support flushing ethernet rules

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

pfctl: Document displaying Ethernet rules

Document the new 'pfctl -s ether' functionality.

Reviewed by: bcr
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D31750

pf: Support killing 'matching' states

Optionally also kill states that match (i.e. are the NATed state or
opposite direction state entry for) the state we're killing.

See also https://redmine.pfsense.org/issues/8555

Submitted by: Steven Brown
Reviewed by: bcr (man page)
Obtained from: https://github.com/pfsense/FreeBSD-src/pull/11/
MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D30092

pf: Allow states to by killed per 'gateway'

This allows us to kill states created from a rule with route-to/reply-to
set. This is particularly useful in multi-wan setups, where one of the
WAN links goes down.

Submitted by: Steven Brown
Obtained from: https://github.com/pfsense/FreeBSD-src/pull/11/
MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D30058

pf: Return non-zero from 'status' if pf is not enabled

In the pf rc.d script the output of `/etc/rc.d/pf status` or `/etc/rc.d/pf
onestatus` always provided an exit status of zero. This made it fiddly to
programmatically determine if pf was running or not.

Return a non-zero status if the pf module is not loaded, extend pfctl to have
an option to return an error status if pf is not enabled.

PR: 228632
Submitted by: James Park-Watt <jimmypw AT gmail.com>
MFC after: 1 week

Note the version PF first appeared in FreeBSD & from which version it was ported from.
Address the contractions raised by igor.

PR: 212574
Approved by: bcr (mentor)
MFC after: 4 days
Differential Revision: https://reviews.freebsd.org/D8105

mdoc: remove superfluous paragraph macros.

Minor mdoc fix.

o Create directory sys/netpfil, where all packet filters should
reside, and move there ipfw(4) and pf(4).

o Move most modified parts of pf out of contrib.

Actual movements:

sys/contrib/pf/net/*.c -> sys/netpfil/pf/
sys/contrib/pf/net/*.h -> sys/net/
contrib/pf/pfctl/*.c -> sbin/pfctl
contrib/pf/pfctl/*.h -> sbin/pfctl
contrib/pf/pfctl/pfctl.8 -> sbin/pfctl
contrib/pf/pfctl/*.4 -> share/man/man4
contrib/pf/pfctl/*.5 -> share/man/man5

sys/netinet/ipfw -> sys/netpfil/ipfw

The arguable movement is pf/net/*.h -> sys/net. There are
future plans to refactor pf includes, so I decided not to
break things twice.

Not modified bits of pf left in contrib: authpf, ftp-proxy,
tftp-proxy, pflogd.

The ipfw(4) movement is planned to be merged to stable/9,
to make head and stable match.

Discussed with: bz, luigi