Debian: libgtp is libgtp2 for some time, not libgtp1 anymore

In Change-Id Ie631880155513b1b78d1e9dd473dc5dc50e05943 we changed
LIBVERSION but didn't update debian/control.

Change-Id: I7a1349e9609cb455c0fe9d63d085e7c44dff96ef

debian/control

@@ -22,7 +22,7 @@ Description: Osmocom Gateway GPRS Support Node (GGSN)
  operators as the interface between the Internet and the rest of the
  mobile network infrastructure.
 
-Package: libgtp1
+Package: libgtp2
 Architecture: any
 Multi-Arch: same
 Section: libs
@@ -41,7 +41,7 @@ Architecture: any
 Multi-Arch: same
 Section: libdevel
 Depends: ${misc:Depends},
-         libgtp1 (= ${binary:Version})
+         libgtp2 (= ${binary:Version})
 Description: Development files for libgtp
  OsmoGGSN is a Gateway GPRS Support Node (GGSN). It is used by mobile
  operators as the interface between the Internet and the rest of the
@@ -54,6 +54,6 @@ Package: osmo-ggsn-dbg
 Section: debug
 Architecture: any
 Priority: extra
-Depends: ${shlibs:Depends}, ${misc:Depends}, libgtp1 (= ${binary:Version}), osmo-ggsn (= ${binary:Version})
+Depends: ${shlibs:Depends}, ${misc:Depends}, libgtp2 (= ${binary:Version}), osmo-ggsn (= ${binary:Version})
 Multi-Arch: same
 Description: Debug symbols for OsmoGGSN