net/mlx5e: Fix MACsec initial packet number

Currently when creating MACsec object, next_pn which represents
the initial packet number (PN) is considered only in TX flow.
The above causes mismatch between TX and RX initial PN which
is reflected in packet drops.
Fix by considering next_pn in RX flow too.

Fixes: aae3454e ("net/mlx5e: Add MACsec offload Rx command support")
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>