BFD liveness detection

New detection-time threshold and transmit-interval threshold configuration statements are available at various levels of the [edit protocols] and [edit routing-options] hierarchy levels. SNMP traps are sent when the detection time or transmit interval exceeds the configured values. With the addition of these statements, the minimum-transmit-interval configuration statement has been deprecated. A new BFD MIB (mib-jnx-bfd.txt) has been added to support the SNMP trap feature.