csd_bs: force rate adaptation mode for CSD calls to V.110

Certain calls (seen on very old Nokias) won't have the rate adaptation flag
set on "analog" CSD calls. The field for the intermediate rate (after RA) is
still filled correctly.
Workaround this by setting the RA to V.110 whenever the RA is unset but an
intermediate rate is specified.

Change-Id: I5b3e5649fe071636f1becddfbfee06f9175a5f17
---
M src/libmsc/csd_bs.c
1 file changed, 20 insertions(+), 0 deletions(-)

diff --git a/src/libmsc/csd_bs.c b/src/libmsc/csd_bs.c
index caea057..ab0b643 100644
--- a/src/libmsc/csd_bs.c
+++ b/src/libmsc/csd_bs.c
@@ -236,6 +236,11 @@
 	enum gsm48_bcap_user_rate rate = cap->data.user_rate;
 	bool async = cap->data.async;
 
+	/* 3.1kHz CSD calls won't have the rate adaptation field set
+	   but do require rate adaptation. */
+	if (cap->data.interm_rate && !ra)
+		ra = GSM48_BCAP_RA_V110_X30;
+
 	if (ra == GSM48_BCAP_RA_V110_X30 && async && transp) {
 		switch (rate) {
 		case GSM48_BCAP_UR_300:

