bts_*: Add ready_for_pcu API

This is required to start osmo-pcu after osmo-bts is already setup and
activated. Otherwise osmo-pcu ends after connecting to socket with:
"pcu_l1_if.cpp:416 BTS not available"

Change-Id: I7209589f60bda63094336e417638906be5e273c4
diff --git a/src/osmo_gsm_tester/templates/osmo-bts-sysmo.cfg.tmpl b/src/osmo_gsm_tester/templates/osmo-bts-sysmo.cfg.tmpl
index 69f7ac1..c9dde86 100644
--- a/src/osmo_gsm_tester/templates/osmo-bts-sysmo.cfg.tmpl
+++ b/src/osmo_gsm_tester/templates/osmo-bts-sysmo.cfg.tmpl
@@ -9,6 +9,8 @@
   logging level rll debug
   logging level rr debug
   logging level rsl debug
+  ! Level required by ready_for_pcu(): pcu info
+  logging level pcu info
 !
 phy 0
  instance 0