net: macsec: Expose extended packet number (EPN) properties to macsec offload

Currently macsec invokes HW offload path before reading extended packet
number (EPN) related user properties i.e. salt and short secure channel
identifier (ssci), hence preventing macsec EPN HW offload.
Expose those by moving macsec EPN properties reading prior to HW offload
path.

Signed-off-by: Emeel Hakim <ehakim@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>