Add MGMT_RX_PROCESS test command for hostapd

Add MGMT_RX_PROCESS test command for hostapd

This makes it easier to write hwsim test cases to verify management
frame processing sequences with dropped or modified frames. When
ext_mgmt_frame_handling is used, this new command can be used to request
hostapd to process a received a management frame, e.g., based on
information reported in the MGMT-RX events.

This is more or less identical to the earlier wpa_supplicant commit
4de70e2330c54c32f42a5fc93517d65c0a2c3be9 ('Add MGMT_RX_PROCESS test
command for wpa_supplicant'), but for hostapd.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>