PR feedback from @terencechain: re-use current_epoch definition

specs/capella/p2p-interface.md

@@ -59,10 +59,10 @@ See Capella [state transition document](./beacon-chain.md#beaconblockbody) for f
 
 This topic is used to propagate signed bls to execution change messages to be included in future blocks.
 
-Let `system_clock_epoch` be an epoch number according to the local system clock of a node.
 The following validations MUST pass before forwarding the `signed_bls_to_execution_change` on the network:
 
-- _[IGNORE]_ `system_clock_epoch >= CAPELLA_FORK_EPOCH`.
+- _[IGNORE]_ `current_epoch >= CAPELLA_FORK_EPOCH`,
+  where `current_epoch` is defined by the current wall-clock time.
 - _[IGNORE]_ The `signed_bls_to_execution_change` is the first valid signed bls to execution change received
   for the validator with index `signed_bls_to_execution_change.message.validator_index`.
 - _[REJECT]_ All of the conditions within `process_bls_to_execution_change` pass validation.