mgcp_protocol: refactor request handler array

the various types of MGCP requests are implemented in request handlers
functions. The function pointers to those functions are held in an array
that is used to find the right handler and call it then. The struct used
to model the array is defined somewhat away from the array definition
and there is also a macro in between that does not help to make the code
more understandable. Lets refactor this a bit to have it more distinct.

Change-Id: I2ef167b2ac179d2b0683a27a095f9662fda460bf
Related: SYS#5535
1 file changed