How can I force a rebuild of a package?

I had to modify iptraf src for me.
Updated tar file in dl directory but binary is not rebuilt.
Have alread y deleted src, binaries but still not rebuilt.

What is the correct way to force to rebuild a package without cleaning all?

make packages/net/iptraf-ng/{clean,compile} V=s

If you changed the source then the checksum does not match.
So you have to update the checksum in the Makefile as well.