Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

MFC r323851:
Remove redundant initialization. Don't use variable - just return the value.
Make scan-build happy by casting to 'void *' instead of 'void **'.

Submitted by: pjd@
Found by: scan-build and cppcheck
Sponsored by: Wheel Systems

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Remove the limit on descriptors that can be send in one nvlist.

Submitted by: Mariusz Zaborski

Assert input arguments to buf_send() and buf_recv().

Submitted by: Mariusz Zaborski <oshogbo@FreeBSD.org>

Fix sending empty nvlist.

Submitted by: Mariusz Zaborski <oshogbo@FreeBSD.org>

MFp4 @1189139:

Get rid of the msg_peek() function, which has a problem. If there was less
data in the socket buffer than requested by the caller, the function would busy
loop, as select(2) will always return immediately.

We can just receive nvlhdr now, because some time ago we splitted receive of
data from the receive of descriptors.

MFC after: 1 week

Bring in libnv library for managing name/value pairs. The following types
are currently supported:

- NV_TYPE_NULL - only name, no data;
- NV_TYPE_BOOL - boolean (true or false);
- NV_TYPE_NUMBER - 64bit unsigned integer;
- NV_TYPE_STRING - C string;
- NV_TYPE_NVLIST - nested nvlist;
- NV_TYPE_DESCRIPTOR - file descriptor;
- NV_TYPE_BINARY - binary data.

For detailed documentation and examples see nv(3) manual page.

Sponsored by: The FreeBSD Foundation