[IPv6addr] Use the 32bit wide field of in6_addr in scan_if()
Currently the code relies exlusively on using the 8bit wide
feild of in6_addr. There doesn't really seem to be a good
reason not to use the 32bit one, though I guess there is little
advantage either way.

--HG--
extra : convert_revision : 774ee922abe7dd8381bb69434557064faf48eae3