unit: add test for band fallback

This test uses the same country/country3 values seen by an AP vendor
which causes issues with IWD. The alpha2 is ES (Spain) and the 3rd
byte is 4, indicating to use the E-4. The issue then comes when the
neighbor report claims the BSS is under operating class 3 which is
not part of E-4.

With the fallback implemented, this test will pass since it will
try and lookup only on ES (the EU table) which operating class 3 is
part of.

unit/test-band.c

@@ -670,6 +670,19 @@ static void test_conversions(const void *data)
 	assert(!band_channel_to_freq(192, BAND_FREQ_5_GHZ));
 }
 
+static void test_conversion_fallback(const void *data)
+{
+	enum band_freq band;
+	const uint8_t cc[] = {'E', 'S', 0x04};
+
+	/*
+	 * Without a fallback, this would fail. There is no operclass 3 in the
+	 * global operating table (E-4)
+	 */
+	band = band_oper_class_to_band(cc, 3);
+	assert(band == BAND_FREQ_5_GHZ);
+}
+
 int main(int argc, char *argv[])
 {
 	l_test_init(&argc, &argv);
@@ -736,6 +749,7 @@ int main(int argc, char *argv[])
 	l_test_add("/band/6ghz/freq", test_6ghz_freqs, NULL);
 
 	l_test_add("/band/conversions", test_conversions, NULL);
+	l_test_add("/band/conversion fallback", test_conversion_fallback, NULL);
 
 	return l_test_run();
 }