udp: Don't pass udptable to IPv6 socket lookup functions.

udp: Don't pass udptable to IPv6 socket lookup functions.

Since UDP and UDP-Lite had dedicated socket hash tables for
each, we have had to pass the pointer down to many socket
lookup functions.

UDP-Lite gone, and we do not need to do that.

Let's fetch net->ipv4.udp_table only where needed in IPv6
stack: __udp6_lib_lookup() and __udp6_lib_mcast_deliver().

__udp6_lib_err() is renamed to udpv6_err() as its wrapper
is no longer needed.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260311052020.1213705-14-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>