wimax/i2400m: allow kernel commands to device to be logged too

By running 'echo 1 > /sys/kernel/debug/wimax:wmxX/i2400m/trace_msg_from_user',
the driver will echo to user space all the commands being sent to the
device from user space, along with the responses.

However, this only helps with the commands being sent from user space;
with this patch, the trace hook is moved to i2400m_msg_to_dev(), which
is the single access point for running commands to the device (both by
user space and the kernel driver). This allows better debugging by
having a complete stream of commands/acks and reports.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>