modules: hostap: Fix getting error stations twt capability issue.

1. When external station connects to soft ap, zephyr
   hostap will fill sta_info before sending mgmt event
   to l2 wifi layer.
   sta_info.twt_capable should be filled with external
   station capability rather than soft ap self.
2. Rename hapd_is_twt_capable to
   hapd_get_sta_he_twt_capable.
   Try to get twt_capa form capability of external station
   rather than soft ap.

Signed-off-by: Qiankun Li <qiankun.li@nxp.com>