usb/gadget/NCM: Replace tasklet with softirq hrtimer

usb/gadget/NCM: Replace tasklet with softirq hrtimer

The tx_tasklet tasklet is used in invoke the hrtimer (task_timer) in
softirq context. This can be also achieved without the tasklet but
with HRTIMER_MODE_SOFT as hrtimer mode.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: keescook@chromium.org
Cc: linux-usb@vger.kernel.org
Link: http://lkml.kernel.org/r/20171221104205.7269-36-anna-maria@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>