[nss] warn the users that library cannot be unloaded

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

libknet/crypto_nss.c

@@ -357,6 +357,7 @@ static int init_nss_db(knet_handle_t knet_h)
 void nsscrypto_unload_lib(
 	knet_handle_t knet_h)
 {
+	log_warn(knet_h, KNET_SUB_NSSCRYPTO, "libnss cannot be unloaded at runtime! Please restart your application");
 	return;
 }