Floss: Add request_exec_write_cb in to server_context_map

Some requests don't include a handle as their parameter but
we still need to reply to them with send_response. Give them a
default handle 0 to align with send_response call.

Bug: 269079739
Test: Manually
Tag: #floss
Change-Id: Ibcf8598becc7c163acce56eecf06ad99a9762c37