usr.sbin: 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/

rtsold: Use correct error in llflags_get()

Set errno to EINVAL if the name overflows the buffer, as was done
before commit ecce515d54bc.

Reviewed by: dab, markj
Fixes: ecce515d54bcea54fea03f731aad646c87761d22
MFC after: 1 week
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D34354

rtsold: Fix bugs reported by Coverity

- Avoid leaking a socket if llflags_get() fails.
- Avoid leaking a file handle if rtsold_init_dumpfile() fails.
- Tighten the check in if_nametosdl() which determines whether we failed
to find the specified interface.
- Fix errno handling in an error path in rtsock_open().

MFC after: 1 week

Avoid relying on pollution from libcasper.h.

Reported by: sjg
Sponsored by: The FreeBSD Foundation

Capsicumize rtsol(8) and rtsold(8).

These programs parse ND6 Router Advertisement messages; rtsold(8) has
required an SA, SA-14:20.rtsold, for a bug in this code. Thus, they
are good candidates for sandboxing.

The approach taken is to run the main executable in capability mode
and use Casper services to provide functionality that cannot be
implemented within the sandbox. In particular, several custom services
were required.

- A Casper service is used to send Router Solicitation messages on a
raw ICMP6 socket. Initially I took the approach of creating a
socket for each interface upon startup, and connect(2)ing it to
the all-routers multicast group for the interface. This permits
the use of sendmsg(2) in capability mode, but only works if the
interface's link is up when rtsol(d) starts. So, instead, the
rtsold.sendmsg service is used to transmit RS messages on behalf
of the main process. One could alternately define a service
which simply creates and connects a socket for each destination
address, and returns the socket to the sandboxed process. However,
to implement rtsold's -m option we also need to read the ND6 default
router list, and this cannot be done in capability mode.
- rtsold may execute resolvconf(8) in response to RDNSS and DNSSL
options in received RA messages. A Casper service is used to
fork and exec resolvconf(8), and to reap the child process.
- A service is used to determine whether a given interface's
link-local address is useable (i.e., not duplicated or undergoing
DAD). This information is supplied by getifaddrs(3), which reads
a sysctl not available in capability mode. The SIOCGIFCONF socket
ioctl provides equivalent information and can be used in capability
mode, but I decided against it for now because of some limitations
of that interface.

In addition to these new services, cap_syslog(3) is used to send
messages to syslogd.

Reviewed by: oshogbo
Tested by: bz (previous versions)
MFC after: 2 months
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D17572