Increase timeout in DNS_TIMEOUTS test for ESP8266

The test floods the device with UDP requests (it skips the 100 ms delay to simulate instant timeout). ESP8266 starts responding with "busy p..." message. It needs more time to process the data and recover for subsequent tests.

Author: michalpasztamobica

TESTS/netsocket/dns/asynchronous_dns_timeouts.cpp

@@ -66,6 +66,11 @@ void ASYNCHRONOUS_DNS_TIMEOUTS()
 
     // Give event queue time to finalise before destructors
     ThisThread::sleep_for(2000);
+#ifdef MBED_CONF_ESP8266_TX
+    // This test does a lot of requests on the ESP's sockets.
+    // If subsequents tests start too early they run into "busy p...".
+    ThisThread::sleep_for(10000);
+#endif
 
     nsapi_dns_call_in_set(0);
 }