OpenZFS 2605, 6980, 6902

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>
Ported-by: kernelOfTruth <kerneloftruth@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

OpenZFS-issue: https://www.illumos.org/issues/2605
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/9c3fd12

6980 6902 causes zfs send to break due to 32-bit/64-bit struct mismatch
Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Ported by: Brian Behlendorf <behlendorf1@llnl.gov>

OpenZFS-issue: https://www.illumos.org/issues/6980
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/ea4a67f

Porting notes:
- All rsend and snapshop tests enabled and updated for Linux.
- Fix misuse of input argument in traverse_visitbp().
- Fix ISO C90 warnings and errors.
- Fix gcc 'missing braces around initializer' in
  'struct send_thread_arg to_arg =' warning.
- Replace 4 argument fletcher_4_native() with 3 argument version,
  this change was made in OpenZFS 4185 which has not been ported.
- Part of the sections for 'zfs receive' and 'zfs send' was
  rewritten and reordered to approximate upstream.
- Fix mktree xattr creation, 'user.' prefix required.
- Minor fixes to newly enabled test cases
- Long holds for volumes allowed during receive for minor registration.

include/libzfs.h

@@ -640,6 +640,10 @@ typedef boolean_t (snapfilter_cb_t)(zfs_handle_t *, void *);
 extern int zfs_send(zfs_handle_t *, const char *, const char *,
     sendflags_t *, int, snapfilter_cb_t, void *, nvlist_t **);
 extern int zfs_send_one(zfs_handle_t *, const char *, int, enum lzc_send_flags);
+extern int zfs_send_resume(libzfs_handle_t *, sendflags_t *, int outfd,
+    const char *);
+extern nvlist_t *zfs_send_resume_token_to_nvlist(libzfs_handle_t *hdl,
+    const char *token);
 
 extern int zfs_promote(zfs_handle_t *);
 extern int zfs_hold(zfs_handle_t *, const char *, const char *,
@@ -680,6 +684,12 @@ typedef struct recvflags {
 	/* set "canmount=off" on all modified filesystems */
 	boolean_t canmountoff;
 
+	/*
+	 * Mark the file systems as "resumable" and do not destroy them if the
+	 * receive is interrupted
+	 */
+	boolean_t resumable;
+
 	/* byteswap flag is used internally; callers need not specify */
 	boolean_t byteswap;