Function check_bip65 

pub fn check_bip65(tx_locktime: u32, stack_locktime: u32) -> bool

BIP65 CLTV core check (Orange Paper §5.4.7 / BIP65).

Valid when locktime types match, stack_locktime <= tx_locktime, and the spending input sequence is not 0xffffffff. A zero tx locktime is allowed; (tx=0, stack=0) passes (mainnet block 659901 regression).