gsm690: Fix amr speech bit length table

The table amr_len_by_ft represents the length of the raw AMR speech bits
in bytes. The table is based on the Table found in RFC 4867 ยง3.6, Table 1,
Column "Total speech bits". The number of bits is divided by 8 and then
rounded up to get the number of consumed octets.

An AMR SID frame (including STI and MI) takes up 39 bits, this will
result in 5 octets, not in 7. Lets correct this.

Related: OS#2978
Change-Id: Icf330450981b32be5d1cee5b10aa92bac4cb72f5
diff --git a/src/codec/gsm690.c b/src/codec/gsm690.c
index 1955716..8ab1df1 100644
--- a/src/codec/gsm690.c
+++ b/src/codec/gsm690.c
@@ -216,8 +216,9 @@
 	 92,  31,  52,  65,  86,
 };
 
+/* See also RFC 4867 §3.6, Table 1, Column "Total speech bits" */
 static const uint8_t amr_len_by_ft[16] = {
-	12, 13, 15, 17, 19, 20, 26, 31, 7,  0,  0,  0,  0,  0,  0,  0
+	12, 13, 15, 17, 19, 20, 26, 31, 5,  0,  0,  0,  0,  0,  0,  0
 };
 
 const struct value_string osmo_amr_type_names[] = {