usr.bin: 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/

netlink: use newly-added snl(3) array parsing for handling multipath
routes.

MFC after: 2 weeks

netstat: fix double-free in netlink error code path.

CID: 1504382

netstat: simplify netlink route printing code.

A number of improvements has commited to snl(3) recently.
A notable one is snl(3) build-in parsers for all of the objects
exported by the kernel.

This change updates netlink handling code to the latest available snl(3)
API.

netstat: fix IPv6 link-locals & custom multipath printing.

netstat: export weight for single-path routes.

* Parse and export newly-added NL_RTA_WEIGHT attribute, providing path
weight for a non-multipath route. This fixes a number of tests in
sys/net/routing which rely on this data.
* Remove handling of NL_RTA_KNH_ID in multipath routes, as it is
not provided.
* Improve kernel/user nexthop index export. As a result,
for multipath routes:
* nhg-kidx attribute represents kernel nhg index (always provided)
* nhg-uidx attribute represents user-provided nhg index (if set)
for non-multipath routes:
* nhop-kidx attribute represents kernel nhop index (always provided)
* nhop-udx attribute represents user-provided nexthop index (if set)

netstat: fix format string on 32-bit archs

netstat: make netstat -rn use netlink instead of rtsock

This change switches route listing in netstat to netlink, with fallback to rtsock.
The outputs are mostly identical, with an exception of not showing kernel
nexthop indexes for multipath routes.

Differential Revision: https://reviews.freebsd.org/D36529