Allow packetization vaules > 127

According to the RTP packetization documentation, and the maximum values
listed in AST_FORMAT_LIST, we should support values > that the signed
char array that ast_codec_pref makes available to store the value. All
places in the code treat the framing field as though it were an int
array instaead of a char array anyway, so this just fixes the type of
the array.

(closes issue ASTERISK-18876)
Review: https://reviewboard.asterisk.org/r/1639/
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Merged revisions 348833 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 348845 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@348847 65c4cc65-6c06-0410-ace0-fbb531ad65f3