net: constify dev pointer in misc instance lock helpers

lockdep asserts and predicates can operate on const pointers.
In the future this will let us add asserts in functions
which operate on const pointers like dev_get_min_mp_channel_count().

Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250324224537.248800-4-kuba@kernel.org


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