ping: Unify ping/ping6 statistics section

This is a first step towards a unification/simplification of ping/ping6
(internally). The end goal is to produce a standardized user-facing
output.

Before (ping6):

PING6(56=40+8+8 bytes) 2001:db8::1 --> 2001:db8::2
16 bytes from ::1, icmp_seq=0 hlim=64 time=0.168 ms
16 bytes from ::1, icmp_seq=1 hlim=64 time=0.068 ms

--- 2001:db8::2 ping6 statistics ---
round-trip min/avg/max/std-dev = 0.068/0.118/0.168/0.050 ms

After (ping6):

PING(56=40+8+8 bytes) 2001:db8::1 --> 2001:db8::2
16 bytes from ::1, icmp_seq=0 hlim=64 time=0.168 ms
16 bytes from ::1, icmp_seq=1 hlim=64 time=0.068 ms

--- 2001:db8::2 ping statistics ---
round-trip min/avg/max/stddev = 0.068/0.118/0.168/0.050 ms

This has the nice side-effect of adding units to SIGINFO's statistics,
as printing numbers without units may not be of much help. Also
mentions the fact that these times are round-trip.

Before (ping/ping6 SIGINFO):

2/2 packets received (100.0%) 0.068 min / 0.118 avg / 0.168 max

After (ping/ping6 SIGINFO):

--- <ipv4/ipv6 address> ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.068/0.118/0.168/0.050 ms

In the case of a SIGINFO, the output will be printed to stderr, for both
ping and ping6.

Reviewed by: markj
MFC after: 1 week
Pull Request: https://github.com/freebsd/freebsd-src/pull/863
Differential Revision: https://reviews.freebsd.org/D39126

Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

ping: split the visual part of -f into a new option -.

After this, we'll be able to ping a host and not spam the terminal, and
no flooding will have to be involved. I've been doing this under Linux
as ping -fi1 host.

Reviewed by: rpokala, Pau Amma
Differential Revision: https://reviews.freebsd.org/D34882

ping: fix parsing of options including '4' and '6'

ping uses a two-pass option parser. The first pass determines whether
ipv4 or ipv6 is desired, and the second parses the rest of the options.
But the first pass wrongly detects a '4' or '6' in an option's value as
a request to use ipv6 or ipv6 respectively, for example in an invocation
like "ping -c6 1.2.3.4".

Fix this confusion by including all options in the first round of
parsing, but ignoring those unrelated to ipv4/ipv6 selection.

PR: 258048
Reported by: ghuckriede@blackberry.com
Submitted by: ghuckriede@blackberry.com
MFC after: 2 weeks
Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D32344

Merge ping6 to ping

There is now a single ping binary, which chooses to use ICMP or ICMPv4
based on the -4 and -6 options, and the format of the address.

Submitted by: Ján Sučan <sucanjan@gmail.com>
Sponsored by: Google LLC (Google Summer of Code 2019)
MFC after: Never
Differential Revision: https://reviews.freebsd.org/D21377