Skinny: fix up session logging.

Logging from the skinny session loop was providing some incorrect reasons
for exiting the loop. Cleaned up messages and handling so correct reason
displayed.
........

Merged revisions 405924 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@405925 f38db490-d61c-443f-a65b-d21fe96a405b