UPSTREAM: net: add netdev_sw_irq_coalesce_default_on()

Add a helper for drivers wanting to set SW IRQ coalescing
by default. The related sysfs attributes can be used to
override the default values.

Follow Jakub's suggestion and put this functionality into
net core so that drivers wanting to use software interrupt
coalescing per default don't have to open-code it.

Note that this function needs to be called before the
netdevice is registered.

refs #SWANDROID-15763

Bug: 434987621
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Change-Id: I3e6fbd1e6be35a58aedc4af29fe22842c82d8814
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit d9360708)
Signed-off-by: Danesh Petigara <danesh.petigara@broadcom.com>