Fix for PduParser.java, allows mms recieve on supersonic

mms recieve on supersonic is not working due to changes
in  content disposition parsing in PduParser.java.
This change fixes the if statement which previously ran
if the preference config_mms_content_disposition_support
was true, which it always was.
This change also needs the preference in the device
specific overlay config.xml to be set to false for
affected devices/carriers (Sprint).

Change-Id: I374913fc486718433a1f03082db741045798d789