bridge: vni: Align output columns

bridge: vni: Align output columns

Use fixed column widths to improve readability.

These changes are similar to commit e0c457b1a5a2 ("bridge: Align output
columns").

Before:
$ bridge vni
dev               vni              group/remote
vxlan1             4001
                   4002           10.0.0.1
                   5000-5010
                   16777214-16777215        10.0.0.2
vxlan2             100

After:
$ bridge vni
dev               vni                group/remote
vxlan1            4001
                  4002               10.0.0.1
                  5000-5010
                  16777214-16777215  10.0.0.2
vxlan2            100

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>