net: Push highest priority net_pkt directly to driver

If user has set the priority of the sent net_pkt to highest
priority (NET_PRIORITY_CA) and enabled CONFIG_NET_TC_SKIP_FOR_HIGH_PRIO
option, then push that packet directly to driver instead of TX queue.
This will make the TX sending latency smaller for the high priority
packet. This is not enabled by default.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>