Install an extra hold on the newly allocated synq entry so that it cannot be freed while do_pass_accept_req is running.  This closes a race where do_pass_establish on another CPU (the driver chose a different queue for the new tid) expands the synq entry into a full PCB and then releases the only hold on it, all while do_pass_accept_req is still running.
Install an extra hold on the newly allocated synq entry so that it
cannot be freed while do_pass_accept_req is running.  This closes a race
where do_pass_establish on another CPU (the driver chose a different
queue for the new tid) expands the synq entry into a full PCB and then
releases the only hold on it, all while do_pass_accept_req is still
running.

MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase