iproute: fix tc -iec display of Mibit rates

iproute: fix tc -iec display of Mibit rates

As reported by Thomas Mühlgrabner <muehltom@cable.vol.at>
in http://bugs.debian.org/662979 :

 When showing htb class configuration with "tc -iec class show",
 the output for Mibit is actually the value for bit.
 Example: configure a class with a ceil of 1000Mibit.
 Output states 1048576000 Mibit.

The cause is missing parenteses in the display code of tc....

(Please also note that a lower value of 100Mibit will be displayed
as 102400 Kibit, which I think is kind of ugly.)

Reported-by: Thomas Mühlgrabner <muehltom@cable.vol.at>
Signed-off-by: Andreas Henriksson <andreas@fatal.se>