lib: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\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

librss: simplify some NULL checks.

MFC after: 1 week

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