avoid perpetually sending blobs to peers (#5563)

Fix regression from #4808 where blobs that are already known are issued
ACCEPT verdict, propagating them to peers over and over again.

`validateBlobSidecar` contains the correct IGNORE logic. Moved it above
the expensive checks to retain the performance of the check.

beacon_chain/gossip_processing/eth2_processor.nim

@@ -287,12 +287,7 @@ proc processSignedBlobSidecar*(
 
   # Potential under/overflows are fine; would just create odd metrics and logs
   let delay = wallTime - signedBlobSidecar.message.slot.start_beacon_time
-
-  if self.blobQuarantine[].hasBlob(signedBlobSidecar.message):
-    debug "Blob received, already in quarantine", delay
-    return ValidationRes.ok
-  else:
-    debug "Blob received", delay
+  debug "Blob received", delay
 
   let v =
     self.dag.validateBlobSidecar(self.quarantine, self.blobQuarantine,

beacon_chain/gossip_processing/gossip_validation.nim

@@ -331,6 +331,12 @@ proc validateBlobSidecar*(
   if not (sbs.message.slot > dag.finalizedHead.slot):
     return errIgnore("SignedBlobSidecar: slot already finalized")
 
+  # [IGNORE] The sidecar is the only sidecar with valid signature
+  # received for the tuple (sidecar.block_root, sidecar.index).
+  if blobQuarantine[].hasBlob(sbs.message):
+    return errIgnore(
+      "SignedBlobSidecar: already have blob with valid signature")
+
   # [IGNORE] The block's parent (defined by block.parent_root) has
   # been seen (via both gossip and non-gossip sources) (a client MAY
   # queue blocks for processing once the parent block is retrieved).
@@ -376,12 +382,6 @@ proc validateBlobSidecar*(
     sbs.signature):
     return dag.checkedReject("SignedBlobSidecar: invalid blob signature")
 
-  # [IGNORE] The sidecar is the only sidecar with valid signature
-  # received for the tuple (sidecar.block_root, sidecar.index).
-  if blobQuarantine[].hasBlob(sbs.message):
-    return errIgnore(
-      "SignedBlobSidecar: already have blob with valid signature")
-
   ok()