MFC r323525: MFV r323523: 8331 zfs_unshare returns wrong error code for smb unshare failure

MFC r323524: MFV r316932: 6280 libzfs: unshare_one() could fail with EZFS_SHARENFSFAILED

MFC r305209: MFV r302660: 6314 buffer overflow in dsl_dataset_name

illumos/illumos-gate@9adfa60d484ce2435f5af77cc99dcd4e692b6660
https://github.com/illumos/illumos-gate/commit/9adfa60d484ce2435f5af77cc99dcd4e6
92b6660

https://www.illumos.org/issues/6314
Callers of dsl_dataset_name pass a buffer of size ZFS_MAXNAMELEN, but
dsl_dataset_name copies the datasets' name PLUS the snapshot name to it,
resulting in a max of 2 * ZFS_MAXNAMELEN + '@'.

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Igor Kozhukhov <ikozhukhov@gmail.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Author: Matthew Ahrens <mahrens@delphix.com>

MFC r305207: MFV r302659: 6931 lib/libzfs: cleanup gcc warnings

illumos/illumos-gate@88f61dee20b358671b1b643e9d1dbf220a1d69be
https://github.com/illumos/illumos-gate/commit/88f61dee20b358671b1b643e9d1dbf220a1d69be

https://www.illumos.org/issues/6931
need cleanup:
CERRWARN += -_gcc=-Wno-switch
CERRWARN += -_gcc=-Wno-parentheses
CERRWARN += -_gcc=-Wno-unused-function

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Igor Kozhukhov <ikozhukhov@gmail.com>

MFC r277300 (by smh): Mechanically convert cddl sun #ifdef's to illumos

Since the upstream for cddl code is now illumos not sun, mechanically
convert all sun #ifdef's to illumos #ifdef's which have been used in all
newer code for some time.

Also do a manual pass to correct the use if #ifdef comments as per style(9)
as well as few uses of #if defined(__FreeBSD__) vs #ifndef illumos.

MFC r289362, r289445: 2605 want to resume interrupted zfs send

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed by: Xin Li <delphij@freebsd.org>
Reviewed by: Arne Jansen <sensille@gmx.net>
Approved by: Dan McDonald <danmcd@omniti.com>
Author: Matthew Ahrens <mahrens@delphix.com>

illumos/illumos-gate@9c3fd1216fa7fb02cfbc78a2518a686d54b48ab8

For more info, see:
- slides http://www.slideshare.net/MatthewAhrens/openzfs-send-and-receive
- video https://www.youtube.com/watch?v=iY44jPMvxog
- manpage changes (for zfs resume -s and zfs send -t)
- upcoming talk at the OpenZFS Developer Summit

The TL;DR is:
Use "zfs receive -s" to save the partially received state on failure.
On failure, get the receive token with "zfs get receive_resume_token <fs>"
Resume the send with "zfs send -t <token_value>"

Relnotes: yes

MFC r268469: MFV r268453:

Diff reduction against Illumos.

MFC r268469: MFV r268453:

Diff reduction against Illumos.