ibmvnic: Add stat for tx direct vs tx batched

Allow tracking of packets sent with send_subcrq direct vs
indirect. `ethtool -S <dev>` will now provide a counter
of the number of uses of each xmit method. This metric will
be useful in performance debugging.

Signed-off-by: Nick Child <nnac123@linux.ibm.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241001163531.1803152-1-nnac123@linux.ibm.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>