net: fix LLS debug_smp_processor_id() warning

Our use of sched_clock is OK because we don't mind the side effects
of calling it and occasionally waking up on a different CPU.

When CONFIG_DEBUG_PREEMPT is on, disable preempt before calling
sched_clock() so we don't trigger a debug_smp_processor_id() warning.

Reported-by: Cody P Schafer <devel-lists@codyps.com>
Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>