cangen: set seed value for pseudo random numbers

cangen: set seed value for pseudo random numbers

As pointed out by Andre Naujoks the pseudo random generator should be
initialized with a seed to prevend this ugly behaviour:

$ ./cangen vcan2 -v & ./cangen vcan1 -v
[1] 5995
  vcan2  567#69.98.3C.64.73.48
  vcan1  567#69.98.3C.64.73.48
  vcan2  451#4A.94.E8.2A.EC.58.55.62
  vcan1  451#4A.94.E8.2A.EC.58.55.62
  vcan2  729#BA.58.1B.3D.AB.D7.7E.50
  vcan1  729#BA.58.1B.3D.AB.D7.7E.50
(..)

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>