only check payload hash if not withheld

specs/_features/epbs/p2p-interface.md

@@ -139,7 +139,8 @@ Let `block` be the block with `envelope.beacon_block_root`.
 Let `header` alias `block.body.signed_execution_payload_header.message` (notice that this can be obtained from the `state.signed_execution_payload_header`)
 - _[REJECT]_ `block` passes validation. 
 - _[REJECT]_ `envelope.builder_index == header.builder_index` 
-- _[REJECT]_ `payload.block_hash == header.block_hash`
+- if `envelope.payload_withheld == False` then 
+    - _[REJECT]_ `payload.block_hash == header.block_hash`
 - _[REJECT]_ The builder signature, `signed_execution_payload_envelope.signature`, is valid with respect to the builder's public key.
 
 ###### `payload_attestation_message`