This sets the nLockTime to the tip (and accordingly each input's nSequence to
0xfffffffe) for withdrawal transactions.
Even if the anti fee-sniping argument might not be valid until some time yet,
this makes our regular wallet transactions far less distinguishable from
bitcoind's ones since it now defaults to using native Segwit transactions
(like us). Moreover other wallets are likely to implement this (if they
haven't already).
Changelog-Added: wallet: withdrawal transactions now sets nlocktime to the current tip.
This is ignored in subdaemons which are per-peer, but very useful for
multi-peer daemons like connectd and gossipd.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>