BUG/MINOR: quic: consume Rx datagram even on error

BUG/MINOR: quic: consume Rx datagram even on error

A BUG_ON crash can occur on qc_rcv_buf() if a Rx packet allocation
failed.

To fix this, datagram are marked as consumed even if a fatal error
occured during parsing. For the moment, only a Rx packet allocation
failure could provoke this. At this stage, it's unknown if the datagram
were partially parsed or not at all so it's better to discard it
completely.

This bug was detected using -dMfail argument.

This should be backported up to 2.7.