dsp_process was enhanced to work with alaw and ulaw in addition to slin.
noticed that some functions could be refactored here it is.

Reported by: irroot
Tested by: irroot, mnicholson
Review: https://reviewboard.asterisk.org/r/1304/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@329432 65c4cc65-6c06-0410-ace0-fbb531ad65f3