system-traffic: Fix up FTP tests.

system-traffic: Fix up FTP tests.

Prior to commit b87a5aacefe2 ("datapath: Fix cached ct with helper."),
we were relying on automatic helpers to ensure that FTP connections were
tracked correctly, regardless of the flows that existed in the datapath.
Now, we can drop the automatic helpers in the root namespace and still
have related connections work correctly. Also, the ALG should only be
specified when committing the connection. Update the rules.

Signed-off-by: Joe Stringer <joe@ovn.org>
Acked-by: Jarno Rajahalme <jarno@ovn.org>