macsec: Netlink support of XPN cipher suites (IEEE 802.1AEbw)

Netlink support of extended packet number cipher suites,
allows adding and updating XPN macsec interfaces.

Added support in:
    * Creating interfaces with GCM-AES-XPN-128 and GCM-AES-XPN-256 suites.
    * Setting and getting 64bit packet numbers with of SAs.
    * Setting (only on SA creation) and getting ssci of SAs.
    * Setting salt when installing a SAK.

Added 2 cipher suite identifiers according to 802.1AE-2018 table 14-1:
    * MACSEC_CIPHER_ID_GCM_AES_XPN_128
    * MACSEC_CIPHER_ID_GCM_AES_XPN_256

In addition, added 2 new netlink attribute types:
    * MACSEC_SA_ATTR_SSCI
    * MACSEC_SA_ATTR_SALT

Depends on: macsec: Support XPN frame handling - IEEE 802.1AEbw.

Signed-off-by: Era Mayflower <mayflowerera@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>