ipv6: Add reasons for skb drops to __udp6_lib_rcv

ipv6: Add reasons for skb drops to __udp6_lib_rcv

[ Upstream commit 4cf91f825b2777f81799f98ce32172b829acd1b2 ]

Add reasons to __udp6_lib_rcv for skb drops. The only twist is that the
NO_SOCKET takes precedence over the CSUM or other counters for that
path (motivation behind this patch - csum counter was misleading).

Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 9c02bec95954 ("bpf, net: Support SO_REUSEPORT sockets with bpf_sk_assign")
Signed-off-by: Sasha Levin <sashal@kernel.org>