Fix a memory copying bug in slinfactory which was causing mixmonitor issues.

Reported by: Michael Walton
Tested by: Jonathan Rose
Patches:
    slinfactory.c.ASTERISK-21799.patch uploaded by Michael Walton (license 6502)
(closes issue ASTERISK-21799)
........

Merged revisions 389895 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@389896 f38db490-d61c-443f-a65b-d21fe96a405b