ipv6: udp: constify 'struct net' parameter of socket lookups

Following helpers do not touch their 'struct net' argument.

- udp6_lib_lookup()
- __udp6_lib_lookup()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240802134029.3748005-6-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>