Add incNum() method, so that we don't need to reinvent it in each subclass.
Add incNum() method, so that we don't need to reinvent it in each
subclass.

sippy/rtpproxy,sippy/rtpproxy,dsanders11/rtpproxy,jevonearth/rtpproxy,jevonearth/rtpproxy,jevonearth/rtpproxy,synety-jdebp/rtpproxy,jevonearth/rtpproxy,sippy/rtp_cluster,synety-jdebp/rtpproxy,synety-jdebp/rtpproxy,dsanders11/rtpproxy,sippy/rtp_cluster,synety-jdebp/rtpproxy,dsanders11/rtpproxy,sippy/rtpproxy