debian: Change python3 dependency to native arch

This small fix enables cross compilation using dpkg-buildpackage on multiarch:
https://wiki.debian.org/CrossCompiling#Building_with_dpkg-buildpackage

`apt build-dep -a<arch>` incorrectly installed non-native python for building

Change-Id: I85994447657cda757348855c3ee9978e8c7c2377
diff --git a/debian/control b/debian/control
index cdf26bb..272fe7f 100644
--- a/debian/control
+++ b/debian/control
@@ -17,7 +17,7 @@
                libtalloc-dev,
                libsctp-dev,
                libusb-1.0-0-dev,
-               python3
+               python3:native
 Standards-Version: 3.9.8
 Vcs-Git: git://git.osmocom.org/libosmocore.git
 Vcs-Browser: http://git.osmocom.org/libosmocore/