d/t/control: mark nft -h test as superficial

This checks if the main binary is correctly installed and linked, and that it is usable at the bare
minimum.

But apparently this is considered superficial, so lets mark it that way.

Closes: #969851
Signed-off-by: Arturo Borrero Gonzalez <arturo@debian.org>

debian/tests/control

 Test-Command: nft -h
 Depends: @
-Restrictions: needs-root
+Restrictions: needs-root, superficial
 
 Tests: internaltest-shell.sh
 Depends: kmod, @