Merge pull request #3144 from TheBlueMatt/2024-06-message-flags

(Re-)add handling for `ChannelUpdate::message_flags`

diff --cc fuzz/src/msg_targets/gen_target.sh
Simple merge

diff --cc fuzz/src/msg_targets/mod.rs
Simple merge

diff --cc lightning/src/ln/channel.rs
Simple merge

diff --cc lightning/src/ln/channelmanager.rs
Simple merge

diff --cc lightning/src/ln/functional_test_utils.rs
Simple merge

diff --cc lightning/src/ln/functional_tests.rs
Simple merge

diff --cc lightning/src/ln/msgs.rs
Simple merge

diff --cc lightning/src/util/test_utils.rs
Simple merge