Limit length of bus.desc in output

[dewitpj]

Currently, the bus.desc field is too and pushes the headings out:

Bus ID 0 (Raw USB traffic, all USB buses)	To device	From device
  Device ID 1 :			0.00 kb/s	0.00 kb/s
  Device ID 2 :			14.29 kb/s	7018.16 kb/s
  Device ID 3 :			12.11 kb/s	4589.09 kb/s

Thanks :)