srs{enb,ue}: add rf_dev_sync option to config templates

pass-through the option so they can be used in templates

just concatenate with rf_dev_args for srsLTE eNB/UE, arguments
parsing will handle them

Change-Id: I3818026c159780f29968888f547163cdf730afad
diff --git a/src/osmo_gsm_tester/templates/srsue.conf.tmpl b/src/osmo_gsm_tester/templates/srsue.conf.tmpl
index be75347..284922b 100644
--- a/src/osmo_gsm_tester/templates/srsue.conf.tmpl
+++ b/src/osmo_gsm_tester/templates/srsue.conf.tmpl
@@ -54,7 +54,7 @@
 # For best performance when BW<5 MHz (25 PRB), use the following device_args settings:
 #     USRP B210: send_frame_size=512,recv_frame_size=512
 
-device_args = ${ue.rf_dev_args}
+device_args = ${ue.rf_dev_args},${ue.rf_dev_sync}
 #time_adv_nsamples = auto
 #burst_preamble_us = auto
 #continuous_tx     = auto