Echoserver Rekey Fix

1. wolfSSH_worker() should return WS_REKEYING if receiving a packet.
2. The echoserver's ssh_worker  should wait for another packet when it
   is rekeying.

examples/echoserver/echoserver.c

@@ -1034,6 +1034,9 @@ static int ssh_worker(thread_ctx_t* threadCtx)
                         #endif
                         continue;
                     }
+                    else if (rc == WS_REKEYING) {
+                        continue;
+                    }
                     else if (rc != WS_WANT_READ) {
                         #ifdef SHELL_DEBUG
                             printf("Break:read sshFd returns %d: errno =%x\n",

src/ssh.c

@@ -2423,6 +2423,11 @@ int wolfSSH_worker(WOLFSSH* ssh, word32* channelId)
     }
 
     if (ret == WS_CHAN_RXD) {
+        if (ssh->isKeying) {
+            ssh->error = WS_REKEYING;
+            return WS_REKEYING;
+        }
+
         WLOG(WS_LOG_DEBUG, "Leaving wolfSSH_worker(), "
                            "data received on channel %u", ssh->lastRxId);
     }