Add data test functionality

Add data test functionality

It is now possible to run hwsim_test like data connectivity test through
wpa_supplicant/hostapd control interface if CONFIG_TESTING_OPTIONS=y is
used for the build. Test functionality is enabled/disabled at runtime
with "DATA_TEST_CONFIG <1/0>". The "DATA_TEST_TX <dst> <src> <tos>"
command can be used to request a test frame to be transmitted.
"DATA-TEST-RX <dst> <src>" event is generated when the test frame is
received.

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