msm: ecm_ipa: start Tx queue immediately

Change the flow control implementation of the network
interface to start the TX queue as soon as possible.
When outstanding packets low watermark is hit, call to
netif_wake_queue. This will start the packet transmission in the same
context instead of waiting for network start to schedule
a TX packet transmission.

Change-Id: Ia479cae0ad5c09ddcff6c3ba5fb875fa97f51f5f
Signed-off-by: Talel Shenhar <tatias@codeaurora.org>