net: systemport: Add support for RDMA overflow statistic counter

RDMA overflows can happen if the Ethernet controller does not have
enough bandwidth allocated at the memory controller level, report RDMA
overflows and deal with saturation, similar to the RBUF overflow
counter.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20221028222141.3208429-1-f.fainelli@gmail.com


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