[PKTGEN]: Sleeping function called under lock

pktgen is calling kmalloc GFP_KERNEL and vmalloc with lock held.
The simplest fix is to turn the lock into a semaphore, since the
thread lock is only used for admin control from user context.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Robert Olsson <robert.olsson@its.uu.se>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>