Remove $FreeBSD$: one-line nroff pattern

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

librss: Remove rss_socket_set_rss_bucket()

In preparation for the removal of the IP_RSS_LISTEN_BUCKET socket
option.

PR: 261398 (exp-run)
Reviewed by: glebius
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D38821

librss: Remove rss_sock_set_bindmulti()

In preparation for the removal of the IP(V6)_BINDMULTI option.

PR: 261398 (exp-run)
Reviewed by: glebius
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D38574

PCBGROUP.9: remove obsolete man page

The PCBGROUP option and KPI were removed entirely in 93c67567e015.

Reviewed by: pauamma (manpages), glebius, melifaro
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D38187

[rss] manpage improvements.

Submitted by: gallatin

Add librss, a simple wrapper around RSS APIs so applications can begin auto-tuning.

I've used this in a handful of RSS test applications. It is just some
very simple functions to fetch the RSS configuration, query the per-bucket
CPU set, and mark sockets as local to an RSS bucket. It should be sufficient
for both thread-based and process-based workloads.

(Yes, I wrote a manpage.)

This is based on some early RSS API and wrapper API work I did whilst
I was at Netflix. Thanks to Netflix for the very original work that
spawned this; thanks to Peter Grehan for his feedback about RSS APIs
and thanks to Jack Vogel and Navdeep Parhar for the NIC-facing side of the
APIs. These fed into the simple userland API I wrote up here.

Reviewed by: gallatin