tbf/rlc: Move the moving of V(A) into the V_B code

Move the code that moves the V_B to the first not acked frame. Return
how many indexes the V_B was moved and update the V_A in the caller.
diff --git a/src/rlc.cpp b/src/rlc.cpp
index d33e206..24ffc17 100644
--- a/src/rlc.cpp
+++ b/src/rlc.cpp
@@ -97,3 +97,22 @@
 		}
 	}
 }
+
+int gprs_rlc_v_b::move_window(const uint16_t v_a, const uint16_t v_s,
+				const uint16_t mod_sns, const uint16_t mod_sns_half)
+{
+	int i;
+	uint16_t bsn;
+	int moved = 0;
+
+	for (i = 0, bsn = v_a; bsn != v_s; i++, bsn = (bsn + 1) & mod_sns) {
+		uint16_t index = (bsn & mod_sns_half);
+		if (is_acked(index)) {
+			mark_invalid(index);
+			moved += 1;
+		} else
+			break;
+	}
+
+	return moved;
+}