ibmveth: Reduce default tx queues to 8

ibmveth: Reduce default tx queues to 8

Previously, the default number of transmit queues was 16. Due to
resource concerns, set to 8 queues instead. Still allow the user
to set more queues (max 16) if they like.

Since the driver is virtualized away from the physical NIC, the purpose
of multiple queues is purely to allow for parallel calls to the
hypervisor. Therefore, there is no noticeable effect on performance by
reducing queue count to 8.

Fixes: d926793c1de9 ("ibmveth: Implement multi queue on xmit")
Reported-by: Dave Taht <dave.taht@gmail.com>
Signed-off-by: Nick Child <nnac123@linux.ibm.com>
Link: https://lore.kernel.org/r/20221107203215.58206-1-nnac123@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>