increase required libosmocore version

osmo-remsim depends on a variety of modern libosmocore features,
and now that libosmocore 1.6.0 has been tagged, we can finally depend
on a more recent minimum version.

Change-Id: Ic3cb86b5be524f15d118bcb7ec1947608fbbb034
diff --git a/debian/control b/debian/control
index bdae589..faef9ee 100644
--- a/debian/control
+++ b/debian/control
@@ -9,7 +9,7 @@
                pkg-config,
                osmo-gsm-manuals-dev,
                libcsv-dev,
-               libosmocore-dev (>= 1.3.0),
+               libosmocore-dev (>= 1.6.0),
                libosmo-abis-dev,
                libosmo-simtrace2-dev,
                libpcsclite-dev,