cdc_ncm: reduce driver latency in the data path

Changes:
- use high resolution timer
  latency became approx. 10-15 times less than before
- use taklet for sending remaining data in tx path
Tested on Intel/ARM.

Reviewed-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Tested-by: Dmitry Tarnyagin <Dmitry.Tarnyagin@stericsson.com>
Signed-off-by: Alexey Orishko <alexey.orishko@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>