Reports the current lifecycle state of this site-to-site VPN tunnel: active, idle, phase1, down, or destroy, mirroring the same state values used for remote-access sessions. Because it's writable, an admin can force-clear a tunnel stuck mid-negotiation by setting it to destroy(4), the standard remedy for a site-to-site tunnel that's hung in phase1 and won't renegotiate cleanly on its own. Example: a branch-office tunnel stuck at tunnelState phase1(130) for an extended period, rather than reaching active(3), is a concrete candidate for a manual reset via this object rather than waiting out a retry timer.