[wlan] Fix data send rate against legacy APs

WLAN-856 #done

Test:
- Manually verify that ralink can connect to an old router running
  protected network (previously AP would ignore EAPOL frames)
- Ran `wlan_client_mlme_unittest` and `wlan_ap_mlme_unittest`

Change-Id: Id87983321bab274dafdb55ea8d31cb0fc2c4580c
7 files changed