pjsip.conf: privkey_file should be priv_key_file, mediaencryption=yes should...

pjsip.conf: privkey_file should be priv_key_file, mediaencryption=yes should be mediaencryption=sdes

privkey_file was missed in the snake case update. An example included an invalid value for the mediaencryption option.
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Merged revisions 414780 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@414781 65c4cc65-6c06-0410-ace0-fbb531ad65f3