nmap: Migrate to python3

nmap: Migrate to python3

- Added PYTHON=python3 prior to configure. This then builds nmap with
   python3.
- ndiff is written as python2 only and currently no patches to make it
   work wih python3 have been accepted by the nmap team. It looks like ndiff
   will stay as it is for some time so ndiff will be removed from the nmap
   package install.
- Added --without-ndiff to configure so nmap is built without ndiff
- Updated rootfile

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>