FreeSWITCH-FS-6836

Merge pull request #278 in FS/freeswitch from ~ARTURZ/freeswitch:FS-7640-wraparound-proof-comparisions to master

* commit '822cbefc4a1467d10ce2694c6fea61b4a7ffe3b3':
  FS-7640 Fix some comparisions in switch_rtp.c to be wraparound proof