ANDROID: selinux: modify RTM_GETLINK permission

Map the permission gating RTM_GETLINK messages to a new permission so
that it can be distinguished from the other netlink route permissions
in selinux policy.

While the kernel supports the new nlmsg extended permission, the policy
does not yet contain the new rules. Keep the support for the
Android-specific policy until the new policy lands.

Bug: 392913234
Bug: 353255679
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Signed-off-by: Thiébaud Weksteen <tweek@google.com>
Change-Id: I83c9b693009a49aa1c7a18102f1b8cea24cd55ee