message: make MAX_BIP125_RBF_SEQUENCE constexpr
diff: class CTransaction;
  -static const uint32_t MAX_BIP125_RBF_SEQUENCE = 0xfffffffd;
  +static constexpr uint32_t MAX_BIP125_RBF_SEQUENCE{0xfffffffd};
  /** Check whether the sequence numbers on this transaction are signaling opt-in to replace-by-fee,
  * according to BIP 125. Allow opt-out of transaction replacement by setting nSequence >
  