On a lightly loaded 24Kc, as measured by 'openssl speed sha1', shows between
27% and 120% speedup depending on block size.
SHA1 is notably used in Transmission for piece verification.
Patch by Catalin Patulea
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@33531 3c298f89-4303-0410-b956-a3cf2f4a3e73
