res_fax: Comment out default settings from res_fax.conf.

Comment out many settings in res_fax.conf.sample. The defaults are set in
res_fax.c, so setting the same value in sample config does nothing but make
the sample config more fragile.

(closes issue ASTERISK-23231)
Reported by: David Brillert
Review: https://reviewboard.asterisk.org/r/3261/
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Merged revisions 409052 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 409053 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 409054 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@409055 65c4cc65-6c06-0410-ace0-fbb531ad65f3