From: Bogdan Andrei Iancu <email@example.com>
Max-Forward (maxfwd) Module
Implements all the operations regarding MAX-Forward header, like adding it (if
not present) or decrementing and checking the value of the existent one
If no Max-Forward header is present in the received request, a header will be
added having the original value equal with "max_value". An OK code is returned
by the function.
If a Max-Forward header is already present, its value will be decremented. If
after this operation its value will be positive non-zero, an OK code will be
returned. Otherwise (for a zero value) an error code will be returned.
Note that an error code will be also returned if the SIP message couldn't
be parsed or if the Max-Forwrd header's body invalid (non numerical string or
negative numerical value)