Kuniyuki Iwashima wrote:

UDP-Lite supports the partial checksum and the coverage is
stored in the position of the length field of struct udphdr.

In RX paths, udp4_csum_init() / udp6_csum_init() save the value
in UDP_SKB_CB(skb)->cscov and set UDP_SKB_CB(skb)->partial_cov
to 1 if the coverage is not full.

The subsequent processing diverges depending on the value,
but such paths are now dead.

Also, these functions have some code guarded for UDP:

  * udp_unicast_rcv_skb / udp6_unicast_rcv_skb
  * __udp4_lib_rcv() and __udp6_lib_rcv().

Let's remove the partial csum code and the unnecessary
guard for UDP-Lite in RX.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
v3: Correct ulen < skb->len case in __udp4_lib_rcv()

Reviewed-by: Willem de Bruijn <willemb@google.com>