xfrm: support output_mark for offload ESP packets

Commit 9b42c1f1 ("xfrm: Extend the output_mark") added output_mark
support but missed ESP offload support.

xfrm_smark_get() is not called within xfrm_input() for packets coming
from esp4_gro_receive() or esp6_gro_receive(). Therefore call
xfrm_smark_get() directly within these functions.

Fixes: 9b42c1f1 ("xfrm: Extend the output_mark to support input direction and masking.")
Signed-off-by: Ulrich Weber <ulrich.weber@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>