switch sqlite3 to single-threaded mode

Looking at 'perf top' of osmo-msc under load shows that there's a
significant amount of time spent in terms of locking (mutex,...)
which is useless as osmo-msc is a single-threaded application.

Unfortunately libdbi doesn't provide a mechanism to perform
sqlite3_config(), so we have to do it directly here, introducing an
explicit build-time dependency (and linkage) to libsqlite3.

Related: OS#5559
Change-Id: I5bbea90d28b6d73b64b9e5124ff59304b90a8a75
diff --git a/debian/control b/debian/control
index 0b2ac6b..d9fccfa 100644
--- a/debian/control
+++ b/debian/control
@@ -11,6 +11,7 @@
                pkg-config,
                libdbi-dev,
                libdbd-sqlite3,
+               libsqlite3-dev,
                libsctp-dev,
                libtalloc-dev,
                libsmpp34-dev (>= 1.14.0),