[sr-dev] indicating gruu support

[Juha Heinanen]

daniel,

i noticed that master sr assumes gruu support if ua includes
+sip.instance contact param in register request, because contact in 200
ok response contains gruu params.

according to rfc5627 gruu support is indicated by

Supported: gruu

that is, +sip.instance contact param is not enough.

could you fix this by making supported gruu test before adding gruu
contact params in 200 ok to register request?

-- juha