debian: Require libgtp-dev after the SO version bump

The ABI of libgtp changed and we require a new library now. Drop
the SO_VERSION from the library name and just depend on libgtp-dev.

Change-Id: Ib301b27e2c08fda827b55820389247e27e5e8fc7
diff --git a/debian/control b/debian/control
index 144e649..87b6f07 100644
--- a/debian/control
+++ b/debian/control
@@ -6,7 +6,7 @@
                autotools-dev,
                autoconf-archive,
                pkg-config,
-               libgtp0-dev,
+               libgtp-dev,
                libosmocore-dev,
                libosmo-sccp-dev,
                libdbi0-dev,