ip: dynamically size columns when printing stats

ip: dynamically size columns when printing stats

This change makes ip -s -s output size the columns
automatically. I often find myself using json
output because the normal output is unreadable.
Even on a laptop after 2 days of uptime byte
and packet counters almost overflow their columns,
let alone a busy server.

For max readability switch to right align.

Before:

    RX: bytes  packets  errors  dropped missed  mcast
    8227918473 8617683  0       0       0       0
    RX errors: length   crc     frame   fifo    overrun
               0        0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    691937917  4727223  0       0       0       0
    TX errors: aborted  fifo   window heartbeat transns
               0        0       0       0       10

After:

    RX:  bytes packets errors dropped  missed   mcast
    8228633710 8618408      0       0       0       0
    RX errors:  length    crc   frame    fifo overrun
                     0      0       0       0       0
    TX:  bytes packets errors dropped carrier collsns
     692006303 4727740      0       0       0       0
    TX errors: aborted   fifo  window heartbt transns
                     0      0       0       0      10

More importantly, with large values before:

    RX: bytes  packets  errors  dropped overrun mcast
    126570234447969 15016149200 0       0       0       0
    RX errors: length   crc     frame   fifo    missed
               0        0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    126570234447969 15016149200 0       0       0       0
    TX errors: aborted  fifo   window heartbeat transns
               0        0       0       0       10

Note that in this case we have full shift by a column,
e.g. the value under "dropped" is actually for "errors" etc.

After:

    RX:       bytes     packets errors dropped  missed   mcast
    126570234447969 15016149200      0       0       0       0
    RX errors:           length    crc   frame    fifo overrun
                              0      0       0       0       0
    TX:       bytes     packets errors dropped carrier collsns
    126570234447969 15016149200      0       0       0       0
    TX errors:          aborted   fifo  window heartbt transns
                              0      0       0       0      10

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David Ahern <dsahern@kernel.org>