gsm0808_utils: fix gsm48 multirate to S-bit converter

The function gsm0808_sc_cfg_from_gsm48_mr_cfg() is used to convert a
gsm48 multirate struct into a set of S-bits (S0 to S15). However, the
conversion function currently does not take into account that bit S1
actually stands for four rates at once (Config-NB-Code = 1). Lets make
sure that S1 is only set when the multirate configuration permits all
four required rates.

Change-Id: I6ad531d4e70c2252e32e2bbaca8e14a7ec6d9840
Related: SYS#4470
diff --git a/tests/gsm0808/gsm0808_test.c b/tests/gsm0808/gsm0808_test.c
index 87f5d2a..8f1e299 100644
--- a/tests/gsm0808/gsm0808_test.c
+++ b/tests/gsm0808/gsm0808_test.c
@@ -1902,6 +1902,27 @@
 	cfg.m10_2 = 1;
 	cfg.m12_2 = 1;
 	test_gsm0808_sc_cfg_from_gsm48_mr_cfg_single(&cfg);
+
+	cfg.m4_75 = 1;
+	cfg.m5_15 = 0;
+	cfg.m5_90 = 1;
+	cfg.m6_70 = 0;
+	cfg.m7_40 = 1;
+	cfg.m7_95 = 0;
+	cfg.m10_2 = 0;
+	cfg.m12_2 = 1;
+	test_gsm0808_sc_cfg_from_gsm48_mr_cfg_single(&cfg);
+
+	cfg.m4_75 = 1;
+	cfg.m5_15 = 0;
+	cfg.m5_90 = 1;
+	cfg.m6_70 = 0;
+	cfg.m7_40 = 1;
+	cfg.m7_95 = 0;
+	cfg.m10_2 = 0;
+	cfg.m12_2 = 0;
+	test_gsm0808_sc_cfg_from_gsm48_mr_cfg_single(&cfg);
+	
 }
 
 static void test_gsm48_mr_cfg_from_gsm0808_sc_cfg_single(uint16_t s15_s0)