New option: --force-fax-mode-delay

This release adds a new option --force-fax-mode-delay.

This is used in the case where there is a switch on the other side that detects the CNG and then switches to the fax machine. In the normal case (force-fax-mode-delay is 0 sec) we switch to T.38 mode before the switch has a chance to hear the CNG and then never switches to the fax machine. This option allows us to delay some amount of time, such as 7 seconds, to allow the switch to hear the CNG and switch to the fax machine.