Add flags for escape expand operation

Calling `ssh_options_apply` more times can result in an unwanted behaviour of
expanding the escape characters more times. Adding flags to check if the
expansion was already done on the current string variables.

Signed-off-by: Norbert Pocs <npocs@redhat.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

src/session.c

@@ -115,6 +115,8 @@ ssh_session ssh_new(void)
                           SSH_OPT_FLAG_KBDINT_AUTH |
                           SSH_OPT_FLAG_GSSAPI_AUTH;
 
+    session->opts.exp_flags = 0;
+
     session->opts.identity = ssh_list_new();
     if (session->opts.identity == NULL) {
         goto err;