SELinux: use SECINITSID_NETMSG instead of SECINITSID_UNLABELED for NetLabel

These changes will make NetLabel behave like labeled IPsec where there is an
access check for both labeled and unlabeled packets as well as providing the
ability to restrict domains to receiving only labeled packets when NetLabel is
in use.  The changes to the policy are straight forward with the following
necessary to receive labeled traffic (with SECINITSID_NETMSG defined as
"netlabel_peer_t"):

 allow mydom_t netlabel_peer_t:{ tcp_socket udp_socket rawip_socket } recvfrom;

The policy for unlabeled traffic would be:

 allow mydom_t unlabeled_t:{ tcp_socket udp_socket rawip_socket } recvfrom;

These policy changes, as well as more general NetLabel support, are included in
the latest SELinux Reference Policy release 20070629 or later.  Users who make
use of NetLabel are strongly encouraged to upgrade their policy to avoid
network problems.  Users who do not make use of NetLabel will not notice any
difference.

Signed-off-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: James Morris <jmorris@namei.org>