smack: Check address length before reading address family

KMSAN will complain if valid address length passed to bind()/connect()/
sendmsg() is shorter than sizeof("struct sockaddr"->sa_family) bytes.

Also, since smk_ipv6_port_label()/smack_netlabel_send()/
smack_ipv6host_label()/smk_ipv6_check()/smk_ipv6_port_check() are not
checking valid address length and/or address family, make sure we check
both. The minimal valid length in smack_socket_connect() is changed from
sizeof(struct sockaddr_in6) bytes to SIN6_LEN_RFC2133 bytes, for it seems
that Smack is not using "struct sockaddr_in6"->sin6_scope_id field.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>