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/

Fix incorrect error message in iovctl

If the iovctl command was invoked with only the -C flag, the user would
receive a message claiming that they needed to also supply either the
-d flag or the -f flag. However, in the case of the -C mode, only the
-f flag is acceptable. Correct this error message in this case.

PR: 222050
Submitted by: Heinz N. Gies
Reported by: Heinz N. Gies
MFC after: 1 week

Clean up repeated "All rights reserved"

Let the nv.h and dnv.h includes be only in sys directory.

Change consumers to include those files from sys.
Add duplicated files to ObsoleteFiles.

Approved by: pjd (mentor)

Approved, oprócz użycie RESTORE_ERRNO() do ustawiania errno.

Change the nvlist_recv() function to take additional argument that
specifies flags expected on the received nvlist. Receiving a nvlist with
different set of flags than the ones we expect might lead to undefined
behaviour, which might be potentially dangerous.

Update consumers of this and related functions and update the tests.

Approved by: pjd (mentor)

Update man page for nvlist_unpack, nvlist_recv, nvlist_xfer, cap_recv_nvlist
and cap_xfer_nvlist.

Reviewed by: AllanJude
Approved by: pjd (mentor)

Add main() for iovctl and hook iovctl into build

Differential Revision: https://reviews.freebsd.org/D87
Reviewed by: jhb
MFC after: 1 month
Sponsored by: Sandvine Inc.