ip-link: add switch to show human readable output

ip-link: add switch to show human readable output

Byte and packet count can increase to really big numbers. This adds a
switch to show human readable output.

4: wl: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DORMANT group default qlen 1000
    link/ether 00:de:ad:be:ee:ef brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast
    1523846973 3969051  0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    8710088361 6077735  0       0       0       0
4: wl: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DORMANT group default qlen 1000
    link/ether 00:de:ad:be:ee:ef brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast
    1.5G       3.9M     0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    8.7G       6.0M     0       0       0       0