mgcp_trunk: use unsigned int instead of int as trunk_nr

the trunk_nr is in struct mgcp_trunk. The trunk number can not be
negative and there is no magic value that makes use of the fact that it
could be negative. Lets use unsigned int to make this less irretating.

Change-Id: I5d0e1d76adb8c92d84331a0aca2496908e41d621
Related: SYS#5535
7 files changed