Add new config option to control AMI alarm event reporting in chan_dahdi.

Add new config option to control AMI alarm event reporting in chan_dahdi.

New config parameter "reportalarms" added in chan_dahdi.conf which supports the
following possible values:
"channels": report each channel alarms (current behavior, default for backward compatibility)
"spans": report an "SpanAlarm" event when the span of any configured channel is alarmed
"all": report channel and span alarms (aggregated behavior)
"none": do not report any alarms

(closes issue #16709)
Reported by: nahuelgreco
Patches:
      chan_dahdi.c.reportalarms.patch uploaded by nahuelgreco (license 162)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@250392 65c4cc65-6c06-0410-ace0-fbb531ad65f3