libwebsockets

sspc: handle loss of proxy manifesting itself as 0 length rx

If the client library loses the proxy connection, it can receive
an endless stream of 0 length rx instead of understanding that
the UDS peer has gone.

Handle that correctly so the client reacts to the loss of the
proxy link by trying to reacquire it.

Adapt the sspc state to be suitable for retry in that case,
by dropping any dsh and letting the logical ss know that he
is DISCONNECTED, if he thought he was CONNECTED.