Update spec from phw's comments.

     "TOR_PT_OUTBOUND_BIND_ADDRESS"

       Specifies an IP address that the PT proxy or server SHOULD use as source

       address for outgoing IP connections. This feature allows people with multiple

       network interfaces to specify explicitly which interface they prefer the PT to

       use.

       Specifies an IP address that the PT proxy SHOULD use as source address for

       outgoing IP packets. This feature allows people with multiple network

       interfaces to specify explicitly which interface they prefer the PT proxy to use.

       If this value is unset or empty the PT MUST use the default source

       If this value is unset or empty, the PT proxy MUST use the default source

       address for outgoing connections.

       This setting MUST be ignored for connections to