Respond to INFO requests in dialog

[wakamoleguy]

Currently, we ignore non-DTMF INFO requests. Applications such as FreeSWITCH send INFO packets in dialogs. We should acknowledge their receipt with a 200 Okay.

[etamme]

In a naive implementation one can simply follow the rules for responding in:

https://tools.ietf.org/html/rfc2976#page-5

"If a server receives an INFO request with a body it understands,
but it has no knowledge of INFO associated processing rules for
the body, the body MAY be rendered and displayed to the user. The
INFO is responded to with a 200 OK.

If the INFO request contains a body that the server does not
understand then, in the absence of INFO associated processing
rules for the body, the server MUST respond with a 415 Unsupported
Media Type message."

[james-criscuolo]

I looked at the commit, looks fine. It was very odd that the DTMF test would suddenly start breaking, but I reintroduced it and added the 415 case as a test as well.

[josephfrazier]

merged at 44f543c