It is likely that the SID for the same PKey will be requested many
times. To reduce the time to modify QPs and process MADs use a cache to
store PKey SIDs.

This code is heavily based on the "netif" and "netport" concept
originally developed by James Morris <jmorris@redhat.com> and Paul Moore
<paul@paul-moore.com> (see security/selinux/netif.c and
security/selinux/netport.c for more information)
Signed-off-by: NDaniel Jurgens <danielj@mellanox.com>
Acked-by: NDoug Ledford <dledford@redhat.com>
Signed-off-by: NPaul Moore <paul@paul-moore.com>