Corrected crypto tag in SDP ANSWER for SRTP. (again)

The original fix (r380043) for getting Asterisk to respond with the correct
tag overlooked some corner cases, and the fact that the same code is in 1.8.

This patch moves the building of the crypto line out of
sdp_crypto_process(). Instead, it merely copies the accepted tag. The call to
sdp_crypto_offer() will build the crypto line in all cases now, using a tag of
"1" in the case of sending offers.

(closes issue ASTERISK-20849)
Reported by: José Luis Millán
Review: https://reviewboard.asterisk.org/r/2295/
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Merged revisions 380347 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@380350 f38db490-d61c-443f-a65b-d21fe96a405b
chan_agent: Prevent multiple channels from logging in as the same agent.

Multiple channels logging in as the same agent can result in dead channels
waiting for a condition signal that will never come because another
channel thread stole it.  A symptom is chan_sip repeatedly generating
warning messages about rescheduling autodestruction of dialogs with an
agent channel owner.

* Made only login_exec() (the app AgentLogin) clear the agent_pvt->chan
pointer to prevent multiple channels from logging in as the same agent.
agent_read(), agent_call(), and agent_set_base_channel() no longer
disconnect the agent channel from the agent_pvt.  This also eliminates the
need to keep checking for agent_pvt->chan being NULL.

* Made agent_hangup() not wake up the AgentLogin agent thread until it is
done.

* Made agent_request() not able to get the agent until he has logged in
and any wrapup time has expired.

* Made agent_request() use ast_hangup() instead of agent_hangup() to
correctly dispose of a channel.

* Removed agent_set_base_channel().  Nobody calls it and it is a bad thing
in general.

* Made only agent_devicestate() determine the current device state of an
agent.  Note: Agent group device states have never been supported.

Review: https://reviewboard.asterisk.org/r/2260/
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Merged revisions 380364 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@380384 f38db490-d61c-443f-a65b-d21fe96a405b