Issue #25114, asyncio: add ssl_object extra info to SSL transports

This info is required on Python 3.5 and newer to get specific information on
the SSL object, like getting the binary peer certificate (instead of getting
it as text).

Lib/asyncio/selector_events.py

@@ -843,6 +843,7 @@ class _SelectorSslTransport(_SelectorTransport):
         self._extra.update(peercert=peercert,
                            cipher=self._sock.cipher(),
                            compression=self._sock.compression(),
+                           ssl_object=self._sock,
                            )
 
         self._read_wants_write = False