crypto: af_alg - properly label AF_ALG socket

crypto: af_alg - properly label AF_ALG socket

Th AF_ALG socket was missing a security label (e.g. SELinux)
which means that socket was in "unlabeled" state.

This was recently demonstrated in the cryptsetup package
(cryptsetup v1.6.5 and later.)
See https://bugzilla.redhat.com/show_bug.cgi?id=1115120

This patch clones the sock's label from the parent sock
and resolves the issue (similar to AF_BLUETOOTH protocol family).

Cc: [email protected]
Signed-off-by: Milan Broz <[email protected]>
Acked-by: Paul Moore <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>