Revert "net: macsec: update SCI upon MAC address change."

This reverts commit 6fc498bc.

Commit 6fc498bc states:

    SCI should be updated, because it contains MAC in its first 6
    octets.

That's not entirely correct. The SCI can be based on the MAC address,
but doesn't have to be. We can also use any 64-bit number as the
SCI. When the SCI based on the MAC address, it uses a 16-bit "port
number" provided by userspace, which commit 6fc498bc overwrites
with 1.

In addition, changing the SCI after macsec has been setup can just
confuse the receiver. If we configure the RXSC on the peer based on
the original SCI, we should keep the same SCI on TX.

When the macsec device is being managed by a userspace key negotiation
daemon such as wpa_supplicant, commit 6fc498bc would also
overwrite the SCI defined by userspace.

Fixes: 6fc498bc

 ("net: macsec: update SCI upon MAC address change.")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://lore.kernel.org/r/9b1a9d28327e7eb54550a92eebda45d25e54dd0d.1660667033.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>