tcpsso: support TIME_WAIT state

TCP endpoints in TIME_WAIT are not handled in a special way anymore.
Therefore, they can be handled now by tcpsso.

Reviewed by: rscheff
MFC after: 1 week
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D43351

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

tcp_sso: add support for TCP_MAXUNACKTIME

Reported by: rscheff@
Reviewed by: rscheff@
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D36802

usr.sbin: add tcpsso

tcpsso is a command line tool to apply a socket option to an
existing TCP endpoint, which is identified by the inp_gencnt.
tcpsso can be used, for example, to switch the congestion control
module or the TCP stack.

Reviewed by: rrs, rscheff, debdrup, pau amma
Relnotes: yes
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D34139