[sr-dev] indicating gruu support

[Juha Heinanen]

Olle E. Johansson writes:

> Note that +sip.instance is also used in SIP outbound.

yes, i know, but in order to use it for gruu, supported gruu MUST be
included:

   When a UA compliant to this specification generates a REGISTER
   request (initial or refresh), it MUST include the Supported header
   field in the request.  The value of that header field MUST include
   "gruu" as one of the option tags.  This alerts the registrar for the
   domain that the UA supports the GRUU mechanism.

-- juha