Revert "net/mlx5e: macsec: use update_pn flag instead of PN comparation"

This reverts commit 89be6ad3 which is
commit fde2f2d7 upstream.

It breaks the Android ABI so revert it for now, if it is needed in the
future, it can be brought back in an ABI-safe way.

Bug: 161946584
Change-Id: Icb4a02c431ae7caeb4669c205d016e991b7d935a
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>