test: use site_id 1801 in ipa BTS example

Thus we can use it with the example file for openBSC under
doc/examples/nanobts/openbsc.cfg.
diff --git a/tests/e1inp_ipa_bts_test.c b/tests/e1inp_ipa_bts_test.c
index d2a21f9..2c03d94 100644
--- a/tests/e1inp_ipa_bts_test.c
+++ b/tests/e1inp_ipa_bts_test.c
@@ -233,7 +233,7 @@
 int main(void)
 {
 	struct ipaccess_unit bts_dev_info = {
-		.site_id	= 0,
+		.site_id	= 1801,
 		.bts_id		= 0,
 		.trx_id		= 0,
 		.unit_name	= "testBTS",