macsec: MACsec SCI assignment for ES = 0

macsec: MACsec SCI assignment for ES = 0

According to 802.1AE standard, when ES and SC flags in TCI are zero,
used SCI should be the current active SC_RX. Current code uses the
header MAC address. Without this patch, when ES flag is 0 (using a
bridge or switch), header MAC will not fit the SCI and MACSec frames
will be discarted.

In order to test this issue, MACsec link should be stablished between
two interfaces, setting SC and ES flags to zero and a port identifier
different than one. For example, using ip macsec tools:

ip link add link $ETH0 macsec0 type macsec port 11 send_sci off
end_station off
ip macsec add macsec0 tx sa 0 pn 2 on key 01 $ETH1_KEY
ip macsec add macsec0 rx port 11 address $ETH1_MAC
ip macsec add macsec0 rx port 11 address $ETH1_MAC sa 0 pn 2 on key 02
ip link set dev macsec0 up

ip link add link $ETH1 macsec1 type macsec port 11 send_sci off
end_station off
ip macsec add macsec1 tx sa 0 pn 2 on key 01 $ETH0_KEY
ip macsec add macsec1 rx port 11 address $ETH0_MAC
ip macsec add macsec1 rx port 11 address $ETH0_MAC sa 0 pn 2 on key 02
ip link set dev macsec1 up

Fixes: c09440f7dcb3 ("macsec: introduce IEEE 802.1AE driver")
Co-developed-by: Andreu Montiel <Andreu.Montiel@technica-engineering.de>
Signed-off-by: Andreu Montiel <Andreu.Montiel@technica-engineering.de>
Signed-off-by: Carlos Fernandez <carlos.fernandez@technica-engineering.de>
Reviewed-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>