lsm: use lsm_prop in security_ipc_getsecid

There may be more than one LSM that provides IPC data for auditing.
Change security_ipc_getsecid() to fill in a lsm_prop structure instead
of the u32 secid.  Change the name to security_ipc_getlsmprop() to
reflect the change.

Cc: audit@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
Cc: selinux@vger.kernel.org
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
[PM: subject line tweak]
Signed-off-by: Paul Moore <paul@paul-moore.com>