Revert "libosmocore/lapd: Fixed handling of sequence errors at lapd_core.c"

This reverts commit 506a3443ba.

src/shared/libosmocore/src/gsm/lapd_core.c

@@ -1497,32 +1497,14 @@ static int lapd_rx_i(struct msgb *msg, struct lapd_msg_ctx *lctx)
 		     "V(R)=%u\n", ns, dl->v_recv);
 		/* discard data */
 		msgb_free(msg);
-		if (dl->seq_err_cond != 1) {
+		if (!dl->seq_err_cond) {
 			/* FIXME: help me understand what exactly todo here
-			*/
 			dl->seq_err_cond = 1;
+			*/
 			lapd_send_rej(lctx, lctx->p_f);
 		} else {
-			/* If there are two subsequent sequence errors received,
-			 * ignore it. (Ignore every second subsequent error.)
-			 * This happens if our reply with the REJ is too slow,
-			 * so the remote gets a T200 timeout and sends another
-			 * frame with a sequence error.
-			 * Test showed that replying with two subsequent REJ
-			 * messages could the remote L2 process to abort.
-			 * Replying too slow shouldn't happen, but may happen
-			 * over serial link between BB and LAPD.
-			 */
-			dl->seq_err_cond = 2;
 		}
-		/* Even if N(s) sequence error, acknowledge to N(R)-1 */
-		/* 5.5.3.1: Acknowlege all transmitted frames up the N(R)-1 */
-		lapd_acknowledge(lctx); /* V(A) is also set here */
-
-		/* Send message, if possible due to acknowledged data */
-		lapd_send_i(lctx, __LINE__);
-
-		return 0;
+		return -EIO;
 	}
 	dl->seq_err_cond = 0;