odhcp6c: fix possible stack corruption when parsing proc if_inet6

odhcp6c: fix possible stack corruption when parsing proc if_inet6

Fix buffer overflow when storing the IPv6 address in addr_buf as
the trailing zero was out of bounds.
Fix possible buffer overflow when storing the interface name in
name as interface name can contain IF_NAMESIZE characters.

Signed-off-by: Hans Dedecker <[email protected]>