Used auth= parameter freed during "sip reload" causes crash.

Used auth= parameter freed during "sip reload" causes crash.

If you use the auth= parameter and do a "sip reload" while there is an
ongoing call.  The peer->auth data points to free'd memory.

The patch does several things:

1) Puts the authentication list into an ao2 object for reference counting
to fix the reported crash during a SIP reload.

2) Converts the authentication list from open coding to AST list macros.

3) Adds display of the global authentication list in "sip show settings".

(closes issue ASTERISK-17939)
Reported by: wdoekes
Patches:
      jira_asterisk_17939_v1.8.patch (license #5621) patch uploaded by rmudgett

Review: https://reviewboard.asterisk.org/r/1303/

JIRA SWP-3526

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@326291 65c4cc65-6c06-0410-ace0-fbb531ad65f3