More robust validation of channel announcement message

[contrun]

https://github.com/contrun/fiber/blob/eeb6ecfa2024dd6c82e3f5ed6a640cd19bf353bf/src/fiber/network.rs#L1745-L1774

While validating whether a channel announcement message is valid, we only checked if the script args is indeed the x only public key in the ChannelAnnouncement message and the ckb capacity is the same to the amount in ChannelAnnouncement. We should also check

• We're actually using the funding contract
• We capacity of udt is indeed the amount in the ChannelAnnouncement message