It is available since Kernel 4.19 and has two parmeters:
1. XFRM ID to map to an SA/SAs
2. Underlying Interface if you want to take advantage of IPSec Hardware Offload
Otherwise it is treated as a normal interface and not like a tunnel (VTI).
I added two attributes to the interface to configure it and otherwise use it as a normal interface.
One example is:
auto ipsec1
iface ipsec1 inet
xfrm-physdev lo
xfrmid 1
