Until now the client called the Linux code directly through the EP
when sending ethernet frames and was not part of the driver's internal
task scheduling. This will lead to problems if the sending code needs
to grab a lock as those depend on running from within a Lx::Task.
Although this has only happend recently when using 8260 devices, this
is an issue that needs to be fix.
This commit addresses the issue by using a dedicated transmit task
in whose context the Linux code sends the ethernet frame or rather
newly allocated skb.
Fixes#2559.
2f32308c0b