bridge: vni: Guard close_vni_port() call

bridge: vni: Guard close_vni_port() call

Currently, the call to open_vni_port() within print_vnifilter_rtm() is
written in a way that is safe if there is a RTM_{NEW,DEL,GET}TUNNEL message
without any VXLAN_VNIFILTER_ENTRY attribute. However the close_vni_port()
call is written in a way that assumes there is always at least one
VXLAN_VNIFILTER_ENTRY attribute within every RTM_*TUNNEL message. At this
time, this assumption is correct. However, the code should be consistent in
its assumptions. Choose the safe approach and fix the asymmetry between the
open_vni_port() and close_vni_port() calls by guarding the latter call with
a check.

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>