linux: Add STF type and convert some if_type to ARPHRD

Convert IFT_BRIDGE and IFT_L2VLAN to ARPHRD_ETHER, and IFT_LOOP
to ARPHRD_LOOPBACK in linux netlink.
Also, add ARPHRD_SIT and convert IFT_STF to it.

Reviewed by: kfv
Differential Revision: https://reviews.freebsd.org/D58573