There are 2 issues fixed by this patch:
  - UDP checksum is computed incorrectly, the used pseudo IP header
    contains transport protocol 6 iso 17
  - on big endian arches the UDP/TCP checksum is incorrectly
    computed when payload length is odd

Signed-off-by: Alin Nastac <alin.nastac@gmail.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name> [refresh patch]