free up existing session in setSSLSession

Summary: Free up the session if its not null before assigning a new one

Reviewed By: shamdor-fb

Differential Revision: D7169809

fbshipit-source-id: fd026e8688525a764b9937c7f4b7bfb0cdece9eb

folly/io/async/AsyncSSLSocket.cpp

@@ -824,6 +824,9 @@ const SSL* AsyncSSLSocket::getSSL() const {
 }
 
 void AsyncSSLSocket::setSSLSession(SSL_SESSION *session, bool takeOwnership) {
+  if (sslSession_) {
+    SSL_SESSION_free(sslSession_);
+  }
   sslSession_ = session;
   if (!takeOwnership && session != nullptr) {
     // Increment the reference count