[HSL] initial support for the HSL 2.75G Femtocell

The HSL Femtocell seems to be a poor man implementation of the
ip.access Abis/IP protocol, but cutting corners wherever possible.

We try to workaround those corners wherever possible...
diff --git a/openbsc/src/libbsc/system_information.c b/openbsc/src/libbsc/system_information.c
index 8a99c56..dc71938 100644
--- a/openbsc/src/libbsc/system_information.c
+++ b/openbsc/src/libbsc/system_information.c
@@ -370,9 +370,14 @@
 	memset(output, GSM_MACBLOCK_PADDING, GSM_MACBLOCK_LEN);
 
 	/* ip.access nanoBTS needs l2_plen!! */
-	if (is_ipaccess_bts(bts)) {
+	switch (bts->type) {
+	case GSM_BTS_TYPE_NANOBTS:
+	case GSM_BTS_TYPE_HSL_FEMTO:
 		*output++ = (l2_plen << 2) | 1;
 		l2_plen++;
+		break;
+	default:
+		break;
 	}
 
 	si5 = (struct gsm48_system_information_type_5 *) output;
@@ -397,9 +402,14 @@
 	memset(output, GSM_MACBLOCK_PADDING, GSM_MACBLOCK_LEN);
 
 	/* ip.access nanoBTS needs l2_plen!! */
-	if (is_ipaccess_bts(bts)) {
+	switch (bts->type) {
+	case GSM_BTS_TYPE_NANOBTS:
+	case GSM_BTS_TYPE_HSL_FEMTO:
 		*output++ = (l2_plen << 2) | 1;
 		l2_plen++;
+		break;
+	default:
+		break;
 	}
 
 	si6 = (struct gsm48_system_information_type_6 *) output;