Skinny: fix up handling of fragmented packets.

Bad offset in reading second or more fragment of skinny packets. Fixed
to offset by char (single byte) rather than size of req.
........

Merged revisions 405982 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@405985 65c4cc65-6c06-0410-ace0-fbb531ad65f3