bridge: vni: Reverse the logic in print_vnifilter_rtm()

bridge: vni: Reverse the logic in print_vnifilter_rtm()

print_vnifilter_rtm() is structured similarly to print_vlan_tunnel_info()
except that in the former, the open_vni_port() call is guarded by a "if
(first)" check whereas in the latter, the open_vlan_port() call is guarded
by a "if (!opened)" check.

Reverse the logic in one of the functions to have the same structure in
both. Since the calls being guarded are "open_...()", "close_...()", use
the "opened" logic structure.

Reviewed-by: Petr Machata <petrm@nvidia.com>
Tested-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Benjamin Poirier <bpoirier@nvidia.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>