The index of protocol on which the BPDU tunnel state
will be set. 'bpdu' represents status of BPDU tunnel.
'stp' represents STP tunnel. 'gvrp' represents GVRP
tunnel. 'igmp' represents IGMP tunnel. STP/GVRP/IGMP
tunnel will start to work only if BPDU tunnel and
STP/GVRP/IGMP tunnel are both enabled.