cifs: writing past end of struct in cifs_convert_address()

"s6->sin6_scope_id" is an int bits but strict_strtoul() writes a long
so this can corrupt memory on 64 bit systems.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>