[IPv6ADDR] Fill in address bytes and use correct endienness

This patch fix up two bugs introduced by my previous series of patches
for ipv6addr

• The result of scanf needs to be copied into addr and when copied it needs to be in network byte order.
• The mask should be in network byte order.

Signed-off-by: Simon Horman <horms@verge.net.au>

--HG--
extra : convert_revision : 8f18f728af07eb04de53f5ae2e6e01e2afbe56db