Fix PTS: TC_GATT_SR_UNS_BI_01_C sends unsupported opcode

In this PTS test, add code to send back an unsupported error response
when an unsupported OpCode is received.

Bug: 79347869
Test: Rerun and pass PTS test
Change-Id: Ibf95dbc18dabbe201850da675c7a1b2739624de9
(cherry picked from commit 8d18b56e)