ws: reporting PONG with pmd enabled

Add a return code NOTHING_WE_SHOULD_DO indicating that the
extension determined by ext-specific means its operation was
disabled on this frame.

https://github.com/warmcat/libwebsockets/issues/2076

lib/core-net/private-lib-core-net.h

@@ -174,6 +174,7 @@ enum pmd_return {
 	PMDR_HAS_PENDING,
 	PMDR_EMPTY_NONFINAL,
 	PMDR_EMPTY_FINAL,
+	PMDR_NOTHING_WE_SHOULD_DO,
 
 	PMDR_FAILED = -1
 };

lib/roles/ws/client-parser-ws.c

@@ -554,6 +554,7 @@ drain_extension:
 				return -1;
 			}
 			if (n == PMDR_DID_NOTHING)
+				/* ie, not PMDR_NOTHING_WE_SHOULD_DO */
 				break;
 #endif
 			lwsl_ext("%s: post inflate ebuf in len %d / out len %d\n",

lib/roles/ws/ext/extension-permessage-deflate.c

@@ -192,10 +192,20 @@ lws_extension_callback_pm_deflate(struct lws_context *context,
 		lwsl_ext(" %s: LWS_EXT_CB_PAYLOAD_RX: in %d, existing in %d\n",
 			 __func__, pmdrx->eb_in.len, priv->rx.avail_in);
 
-		/* if this frame is not marked as compressed, we ignore it */
+		/*
+		 * If this frame is not marked as compressed,
+		 * there is nothing we should do with it
+		 */
 
 		if (!(wsi->ws->rsv_first_msg & 0x40) || (wsi->ws->opcode & 8))
-			return PMDR_DID_NOTHING;
+			/*
+			 * This is a bit different than DID_NOTHING... we have
+			 * identified using ext-private bits in the packet, or
+			 * by it being a control fragment that we SHOULD not do
+			 * anything to it, parent should continue as if we
+			 * processed it
+			 */
+			return PMDR_NOTHING_WE_SHOULD_DO;
 
 		/*
 		 * we shouldn't come back in here if we already applied the

lib/roles/ws/ops-ws.c

@@ -633,6 +633,7 @@ drain_extension:
 				return -1;
 			}
 			if (n == PMDR_DID_NOTHING)
+				/* ie, not PMDR_NOTHING_WE_SHOULD_DO */
 				break;
 #endif
 			lwsl_debug("%s: post ext ret %d, ebuf in %d / out %d\n",
@@ -693,7 +694,8 @@ utf8_fail:
 
 			if (n == PMDR_DID_NOTHING
 #if !defined(LWS_WITHOUT_EXTENSIONS)
-				       	||
+					||
+			    n == PMDR_NOTHING_WE_SHOULD_DO ||
 			    n == PMDR_UNKNOWN
 #endif
 			    )