amd-xgbe: Check per channel DMA interrupt use in main ISR

When using per channel DMA interrupts the transmit interrupt (TI) and the
receive interrupt (RI) are masked off so as to not generate an interrupt
to the main ISR. However, should another interrupt fire for the DMA channel
that is handled by the main ISR the TI/RI bits can still be set. This
will cause the wrong and uninitialized napi structure to be used causing a
panic. Add a check to be sure per channel DMA interrupts are not enabled
before acting on those bit flags.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>