can: fix NOHZ local_softirq_pending 08 warning

can: fix NOHZ local_softirq_pending 08 warning

When using nanosleep() in an userspace application we get a ratelimit warning

NOHZ: local_softirq_pending 08

for 10 times.

The echo of CAN frames is done from process context and softirq context only.
Therefore the usage of netif_rx() was wrong (for years).

This patch replaces netif_rx() with netif_rx_ni() which has to be used from
process/softirq context. It also adds a missing comment that can_send() must
no be used from hardirq context.

Signed-off-by: Oliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: Urs Thuermann <urs@isnogud.escape.de>
Also in mainline.

git-svn-id: svn://svn.berlios.de//socketcan/trunk@1055 030b6a49-0b11-0410-94ab-b0dab22257f2