conntrack: Check all addresses for ephemeral ports.

conntrack: Check all addresses for ephemeral ports.

When fallback to ephemeral ports triggers to find a NAT translation,
it may happen that the full address range is not explored; i.e. if
all ephemeral ports are being used for the address range >= the
first address checked and there are other addresses in the
available range, then they would not be explored for availability.
The likelihood of hitting this condition is rare. The fix is to
reset the first address to the minimum address when starting to
search ephemeral ports.  Found by inspection.

Fixes: 286de2729955 ("dpdk: Userspace Datapath: Introduce NAT Support.")
Signed-off-by: Darrell Ball <dlu998@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>