3740 Poor ZFS send / receive performance due to snapshot hold / release processing
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Christopher Siden <christopher.siden@delphix.com>
	[illumos-gate merge]

commit a7a845e4bf22fd1b2a284729ccd95c7370a0438c
    3740 Poor ZFS send / receive performance due to snapshot hold / release processing