The index of the associated IPsec Phase-1
Tunnel. In case this tunnel was spawned by an
IPsec signaling protocol, this MIB object
contains the value of the object 'cisgIpsSgTunIndex'
defined in CISCO-IPSEC-SIGNALING-MIB in the table
'cisgIpsSgTunnelTable' in the row corresponding to
the control tunnel.
A value of 0 identifies that this Phase-2 tunnel
was setup manually.