esp32/modsocket: Fix getaddrinfo to raise on error.

This commit fixes the behaviour of socket.getaddrinfo on the ESP32 so it
raises an OSError when the name resolution fails instead of returning a []
or a resolution for 0.0.0.0.

Tests are added (generic and ESP32-specific) to verify behaviour consistent
with CPython, modulo the different types of exceptions per MicroPython
documentation.

tests/esp32/resolve_on_connect.py

@@ -0,0 +1,59 @@
+# Test that the esp32's socket module performs DNS resolutions on bind and connect
+import sys
+
+if sys.implementation.name == "micropython" and sys.platform != "esp32":
+    print("SKIP")
+    raise SystemExit
+
+try:
+    import usocket as socket, sys
+except:
+    import socket, sys
+
+
+def test_bind_resolves_0_0_0_0():
+    s = socket.socket()
+    try:
+        s.bind(("0.0.0.0", 31245))
+        print("bind actually bound")
+        s.close()
+    except Exception as e:
+        print("bind raised", e)
+
+
+def test_bind_resolves_localhost():
+    s = socket.socket()
+    try:
+        s.bind(("localhost", 31245))
+        print("bind actually bound")
+        s.close()
+    except Exception as e:
+        print("bind raised", e)
+
+
+def test_connect_resolves():
+    s = socket.socket()
+    try:
+        s.connect(("micropython.org", 80))
+        print("connect actually connected")
+        s.close()
+    except Exception as e:
+        print("connect raised", e)
+
+
+def test_connect_non_existent():
+    s = socket.socket()
+    try:
+        s.connect(("nonexistent.example.com", 80))
+        print("connect actually connected")
+        s.close()
+    except OSError as e:
+        print("connect raised OSError")
+    except Exception as e:
+        print("connect raised", e)
+
+
+test_funs = [n for n in dir() if n.startswith("test_")]
+for f in sorted(test_funs):
+    print("--", f, end=": ")
+    eval(f + "()")