esp: Fix BEET mode inter address family tunneling on GSO

The xfrm{4,6}_beet_gso_segment() functions did not correctly set the
SKB_GSO_IPXIP4 and SKB_GSO_IPXIP6 gso types for the address family
tunneling case. Fix this by setting these gso types.

Fixes: 384a46ea ("esp4: add gso_segment for esp4 beet mode")
Fixes: 7f9e40eb ("esp6: add gso_segment for esp6 beet mode")
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>