app_milliwatt: Timing fix

The Milliwatt application uses incorrect tone timings
that cause it to play the 1004 Hz tone constantly.

This adds an option to enable the correct timing
behavior, so that the Milliwatt application can
be used for milliwatt test lines. The default behavior
remains unchanged for compatability reasons, even
though it is incorrect.

ASTERISK-29575 #close

Change-Id: I73ccc6c6fcaa31931c6fff3b85ad1805b2ce9d8c