CVE-2024-50145: octeon_ep: Add SKB allocation failures handling in __octep_oq_process_rx()

In the Linux kernel, the following vulnerability has been resolved:

octeonep: Add SKB allocation failures handling in octepoqprocessrx()

buildskb() returns NULL in case of a memory allocation failure so handle it inside octepoqprocessrx() to avoid NULL pointer dereference.

octepoqprocessrx() is called during NAPI polling by the driver. If skb allocation fails, keep on pulling packets out of the Rx DMA queue: we shouldn't break the polling immediately and thus falsely indicate to the octepnapipoll() that the Rx pressure is going down. As there is no associated skb in this case, don't process the packets and don't push them up the network stack - they are skipped.

Helper function is implemented to unmmap/flush all the fragment buffers used by the dropped packet. 'allocfailures' counter is incremented to mark the skb allocation error in driver statistics.

Found by Linux Verification Center (linuxtesting.org) with SVACE.