srs{ue,enb,epc}: Disable pcap by default, allow enabling by param

Take the change to fix several small things and support recording pcap
in srsENB.

pcap generation can be enabled with scenario cfg-srs-enable-pcap.

Change-Id: Ia096a9be7efb2123f95115c751e2402fb4fec935
diff --git a/src/osmo_gsm_tester/templates/srsue.conf.tmpl b/src/osmo_gsm_tester/templates/srsue.conf.tmpl
index f7dee03..4a4828e 100644
--- a/src/osmo_gsm_tester/templates/srsue.conf.tmpl
+++ b/src/osmo_gsm_tester/templates/srsue.conf.tmpl
@@ -71,7 +71,7 @@
 # nas_filename: File path to use for NAS packet captures
 #####################################################################
 [pcap]
-enable = true
+enable = ${'true' if ue.enable_pcap else 'false'}
 filename = /tmp/ue.pcap
 nas_enable = false
 nas_filename = /tmp/nas.pcap