Allow external programs to request wpa_radio work items

Allow external programs to request wpa_radio work items

The new control interface command RADIO_WORK can be used by external
programs to request radio allocation slots from wpa_supplicant if
exclusive radio control is needed, e.g., for offchannel operations. If
such operations are done directly to the driver, wpa_supplicant may not
have enough information to avoid conflicting operations. This new
command can be used to provide enough information and radio scheduling
to avoid issues with such cases.

Signed-hostap: Jouni Malinen <j@w1.fi>