3887 Enlarge data buffer in digest/mac to boost performance
Reviewed by: Saso Kiselkov <skiselkov.ml@gmail.com>
Reviewed by: Garrett D'Amore <garrett@damore.org>
Approved by: Dan McDonald <danmcd@nexenta.com>
	[illumos-gate merge]

commit 0e2895337aab790caedfa510ee0ed06ac878344c
    3887 Enlarge data buffer in digest/mac to boost performance