si: Fix range512 encoding

This patch fixes a bug in the range encoder that leads to wrong
encoding when 17 or more ARFCNs are encoded.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/libbsc/arfcn_range_encode.c b/openbsc/src/libbsc/arfcn_range_encode.c
index c52743e..9177546 100644
--- a/openbsc/src/libbsc/arfcn_range_encode.c
+++ b/openbsc/src/libbsc/arfcn_range_encode.c
@@ -256,7 +256,7 @@
 	range512->w15 = HIGH_BITS(w, 15, 6, 6);
 	/* W(16) */
 	range512->w16_hi = HIGH_BITS(w, 16, 5, 2);
-	range512->w16_lo = HIGH_BITS(w, 16, 5, 3);
+	range512->w16_lo = LOW_BITS(w, 16, 5, 3);
 	/* W(17) */
 	range512->w17 = HIGH_BITS(w, 17, 5, 5);