Fixed mmsproxy for Mobinil MMS

See https://www.facebook.com/permalink.php?id=422136431132589&story_fbid=629385780407652

Change-Id: I527b4efff7a30d1c210135040f88c3f63cd68c78
(cherry picked from commit a9c16339a90ad4c47abdfb0a3628bf02df67f656)