macsec: add genl family module alias

This helps tools such as wpa_supplicant can start even if the macsec
module isn't loaded yet.

Fixes: c09440f7 ("macsec: introduce IEEE 802.1AE driver")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>