Remote capability info update for UAC (thanks Bogdan Krakowski for the report)

[nanang]

Reported that PJSIP sends UPDATE to lock to one codec, but remote does not like the UPDATE that finally causing the call to be hung up by PJSIP. From the SIP messages log, the 180 response has UPDATE method in Allow header, but the 200 response has not.

For reference, the spec does specify about SIP header fields contexts:

• headers in a provisional response, ​rfc3261 section-13.2.2.1:

  Header fields present in a provisional
  response are applicable as long as the dialog is in the early state
  (for example, an Allow header field in a provisional response
  contains the methods that can be used in the dialog while this is in
  the early state).
  

• capability info headers in 2xx response, ​rfc3261 section-13.3.1.4

  A 2xx response to an INVITE SHOULD contain the Allow header field and
  the Supported header field, and MAY contain the Accept header field.
  Including these header fields allows the UAC to determine the
  features and extensions supported by the UAS for the duration of the
  call, without probing.
  

[nanang]

In 4171:

Fix #1539: Applied non-strict update of remote capability info after receiving the first 2xx response.