Allow the O_NONBLOCK flag to be reset correctly
sssd set the O_NONBLOCK flag on the LDAP socket twice. First in
set_fd_flags_and_opts(). And the second time in sdap_async_sys_connect_send()
after storing a backup in the local state structure. The backup is later
used to restore the original flags (after connect() succeeded). As NONBLOCK
was already set before it didn't correctly reset that flag.