bridge: Align output columns

bridge: Align output columns

Use fixed column widths to improve readability.

Before:
root@vsid:/src/iproute2# ./bridge/bridge vlan tunnelshow
port    vlan-id tunnel-id
vx0      2       2
         1010-1020       1010-1020
         1030    65556
vx-longname      2       2

After:
root@vsid:/src/iproute2# ./bridge/bridge vlan tunnelshow
port              vlan-id    tunnel-id
vx0               2          2
                  1010-1020  1010-1020
                  1030       65556
vx-longname       2          2

Signed-off-by: Benjamin Poirier <bpoirier@cumulusnetworks.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>