Treat ENOBUFS as success when doing an MRP send. (#9812)

src/messaging/ExchangeMessageDispatch.cpp

@@ -80,7 +80,20 @@ CHIP_ERROR ExchangeMessageDispatch::SendMessage(SessionHandle session, uint16_t
         std::unique_ptr<ReliableMessageMgr::RetransTableEntry, decltype(deleter)> entryOwner(entry, deleter);
 
         ReturnErrorOnFailure(PrepareMessage(session, payloadHeader, std::move(message), entryOwner->retainedBuf));
-        ReturnErrorOnFailure(SendPreparedMessage(session, entryOwner->retainedBuf));
+        CHIP_ERROR err = SendPreparedMessage(session, entryOwner->retainedBuf);
+        if (err == System::MapErrorPOSIX(ENOBUFS))
+        {
+            // sendmsg on BSD-based systems never blocks, no matter how the
+            // socket is configured, and will return ENOBUFS in situation in
+            // which Linux, for example, blocks.
+            //
+            // This is typically a transient situation, so we pretend like this
+            // packet drop happened somewhere on the network instead of inside
+            // sendmsg and will just resend it in the normal MRP way later.
+            ChipLogError(ExchangeManager, "Ignoring ENOBUFS: %" CHIP_ERROR_FORMAT, err.Format());
+            err = CHIP_NO_ERROR;
+        }
+        ReturnErrorOnFailure(err);
         reliableMessageMgr->StartRetransmision(entryOwner.release());
     }
     else