net: ethernet: cortina: Fix budget accounting

In the Linux kernel, the following vulnerability has been resolved: net: ethernet: cortina: Fix budget accounting The gmac_rx() function returns the remaining NAPI budget, but its caller treats the return value as the number of packets received. An idle poll therefore reports a full budget and remains scheduled. Return the number of received packets instead. Preserve the existing free queue refill accounting by adding that count directly; continuing to subtract it from the budget would invert the refill behavior.