esp4/6: Fix GSO path for non-GSO SW-crypto packets

If esp*_offload module is loaded, outbound packets take the
GSO code path, being encapsulated at layer 3, but encrypted
in layer 2. validate_xmit_xfrm calls esp*_xmit for that.

esp*_xmit was wrongfully detecting these packets as going
through hardware crypto offload, while in fact they should
be encrypted in software, causing plaintext leakage to
the network, and also dropping at the receiver side.

Perform the encryption in esp*_xmit, if the SA doesn't have
a hardware offload_handle.

Also, align esp6 code to esp4 logic.

Fixes: fca11ebd ("esp4: Reorganize esp_output")
Fixes: 383d0350

 ("esp6: Reorganize esp_output")
Signed-off-by: Ilan Tayari <ilant@mellanox.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>