Allow testing override for GTK/IGTK RSC from AP to STA

Allow testing override for GTK/IGTK RSC from AP to STA

The new hostapd gtk_rsc_override and igtk_rsc_override configuration
parameters can be used to set an override value for the RSC that the AP
advertises for STAs for GTK/IGTK. The contents of those parameters is a
hexdump of the RSC in little endian byte order.

This functionality is available only in CONFIG_TESTING_OPTIONS=y builds.
This can be used to verify that stations implement initial RSC
configuration correctly for GTK/ and IGTK.

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