This object defines IP address type of the interface
associated with this BFD session.
Only values unknown(0), ipv4(1) or ipv6(2)
have to be supported.
A value of unknown(0) is allowed only when
the outgoing interface is of type point-to-point, or
when the BFD session is not associated with a specific
interface.
If any other unsupported values are attempted in a set
operation, the agent must return an inconsistentValue
error.