gobex: fix automatically including SRM header in CONNECT responses

gobex: fix automatically including SRM header in CONNECT responses

GOEP 2.0 test specification forbids the server to include SRM headers in
CONNECT response:

  "3.16 TP/SRM/BI-03-C Process an OBEX CONNECT request (incorrectly)
  containing a SRM header:

  • Expected Outcome
  Pass Verdict:
  – On receiving the invalid SRM header in the OBEX_CONNECT request, the
  IUT responds with a SUCCESS without a SRM header.
  – OBEX/L2CAP channel is established.
  Fail Verdict:
  – On receiving the invalid SRM header in the OBEX_CONNECT request, the
  IUT does not respond with a SUCCESS and/or includes a SRM header in the
  response.
  – OBEX/L2CAP channel is not established or OBEX/RFCOMM channel is
  established."