[PKTGEN]: proc interface revision

The code to handle the /proc interface can be cleaned up in several places:
* use seq_file for read
* don't need to remember all the filenames separately
* use for_online_cpu's
* don't vmalloc a buffer for small command from user.

Committer note:
This patch clashed with John Hawkes's "[NET]: Wider use of for_each_*cpu()",
so I fixed it up manually.
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NRobert Olsson <robert.olsson@its.uu.se>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NArnaldo Carvalho de Melo <acme@mandriva.com>