fix DH params generation

Remove a return preventing DH params to be generated.
This was introduced by commit 74151247

Tuleap: #792
Change-Id: I131166f7fef655d93425d10da59af04d6104e7f6

src/security/tls_session.cpp

@@ -788,7 +788,6 @@ DhParams
 DhParams::generate()
 {
     using clock = std::chrono::high_resolution_clock;
-    return {};
 
     auto bits = gnutls_sec_param_to_pk_bits(GNUTLS_PK_DH, /* GNUTLS_SEC_PARAM_HIGH */ GNUTLS_SEC_PARAM_HIGH);
     RING_DBG("Generating DH params with %u bits", bits);