srsue.conf.tmpl: reduce nof PHY threads to 2 for ZMQ

we've detected a possible race condition during the Msg3
transmission that caused the thread that sets the Msg3 grant
to be delayed. The PHY worker that executed TTI+2 finished
by that time already and didn't even see the pending UL grant.

This is issue is more likely to happen on loaded system,
for example when running parallel ZMQ jobs. We therefore decided
to reduce the number of parallel PHY workers to 2 so the issue
is circumvented.

Change-Id: Ibdb42a1705d87b6d343201458c8fe397398802bc

src/osmo_gsm_tester/templates/srsue.conf.tmpl

@@ -336,7 +336,9 @@ enable = false
 #snr_ema_coeff       = 0.1
 #snr_estim_alg       = refs
 #pdsch_max_its       = 8    # These are half iterations
-#nof_phy_threads     = 3
+% if ue.rf_dev_type == 'zmq':
+nof_phy_threads     = 2
+% endif
 #equalizer_mode      = mmse
 #sfo_ema             = 0.1
 #sfo_correct_period  = 10