Clear ISDN channel resetting state if the peer continues to use it.

Clear ISDN channel resetting state if the peer continues to use it.

Some ISDN switches occasionally fail to send a RESTART ACKNOWLEDGE in
response to a RESTART request.

* Made the second SETUP received after sending a RESTART request clear the
channel resetting state as if the peer had sent the expected RESTART
ACKNOWLEDGE before continuing to process the SETUP.  The peer may not be
sending the expected RESTART ACKNOWLEDGE.

(issue ASTERISK-19608)
(issue AST-844)
(issue AST-815)
Patches:
      jira_ast_815_v1.8.patch (license #5621) patch uploaded by rmudgett (modified)

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@363687 65c4cc65-6c06-0410-ace0-fbb531ad65f3