MFC r271578,r271579,r271847,r272102,r272843,r273752,r277920,r277921,r277925,r277926,r277927,r279421,r279422,r279423:

r271578 (by pjd):

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

Submitted by: Mariusz Zaborski

r271579 (by pjd):

Use non-recursive algorithm for traversing nvlists. This also removes
the limit on number of nested nvlists.

Submitted by: Mariusz Zaborski

r271847 (by pjd):

Don't use nvl in case of a failure.

Reported by: Coverity
CID: 1238922

r272102 (by pjd):

Document the new nvlist_get_parent() function.

Submitted by: Mariusz Zaborski

r272843 (by pjd):

Fix problem on big endian systems introduced in r271579 - when we were
returning from handling a nested nvlist we were resetting big-endian flag.

Reported by: Kuleshov Aleksey @ yandex.ru
Tested by: Kuleshov Aleksey @ yandex.ru

r273752 (by jmg):

fix typo, properly install a link to nv for nvlist_freev...

r277920 (by pjd):

If moving descriptor or binary data to an nvlist fails, we need to close the
descriptor or free the memory before returning.

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

While here, protect errno, so it won't be overwritted by close(2) or free(3).

r277921 (by pjd):

Modify nvlist_get_parent() API to take additional cookie argument.
This allow for non-recursive iteration over nested nvlists, as in documented
example.

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

r277925 (by pjd):

Handle empty nvlists correctly.

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

r277926 (by pjd):

Add missing nvlist_get_parent(3) link.

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

r277927 (by pjd):

Make gcc happy.

Reported by: bz

r279421 (by rstone):

Make libnv headers includable from C++

Differential Revision: https://reviews.freebsd.org/D1868
Reviewed by: jfv, pjd
Sponsored by: Sandvine Inc.

r279422 (by rstone):

Tests of basic nvlist add functions

Differential Revision: https://reviews.freebsd.org/D1869
Reviewed by: jfv, pjd
Sponsored by: Sandvine Inc.

r279423 (by rstone):

Revert r279422. My "apply patch and commit" script wasn't adding
new files properly.

Pointy hat to: rstone