Bluetooth: L2CAP: Downgrade user_data API error to a warning

When user_data is not zeroed-out, the API returns an error. Downgrade
the API error to a warning log instead.

Introducing this check (#76489) broke a few PTS tests, as user_data is
not initialized by `net_buf_alloc()`. Doing so is in discussion:

#77088

Signed-off-by: Jonathan Rico <jonathan.rico@nordicsemi.no>
(cherry picked from commit 6fa6c4c)

Author: jori-nordic

subsys/bluetooth/host/l2cap.c

@@ -3117,9 +3117,9 @@ static int bt_l2cap_dyn_chan_send(struct bt_l2cap_le_chan *le_chan, struct net_b
 		return -EINVAL;
 	}
 
-	CHECKIF(user_data_not_empty(buf)) {
-		LOG_DBG("Please clear user_data first");
-		return -EINVAL;
+	if (user_data_not_empty(buf)) {
+		/* There may be issues if user_data is not empty. */
+		LOG_WRN("user_data is not empty");
 	}
 
 	/* Prepend SDU length.

tests/bsim/bluetooth/host/l2cap/compile.sh

@@ -13,7 +13,6 @@ source ${ZEPHYR_BASE}/tests/bsim/compile.source
 app=tests/bsim/bluetooth/host/l2cap/many_conns compile
 app=tests/bsim/bluetooth/host/l2cap/general compile
 app=tests/bsim/bluetooth/host/l2cap/userdata compile
-app=tests/bsim/bluetooth/host/l2cap/userdata conf_file=prj_no_checks.conf compile
 app=tests/bsim/bluetooth/host/l2cap/stress compile
 app=tests/bsim/bluetooth/host/l2cap/stress conf_file=prj_nofrag.conf compile
 app=tests/bsim/bluetooth/host/l2cap/stress conf_file=prj_syswq.conf compile

tests/bsim/bluetooth/host/l2cap/userdata/prj_no_checks.conf

@@ -258,20 +258,7 @@ static void test_central_main(void)
 	 */
 	err = bt_l2cap_chan_send(&channel.chan, buf);
 
-	if (has_checks) {
-		/* The stack is supposed to reject `buf` if it has non-null
-		 * user_data.
-		 */
-		if (err == -EINVAL) {
-			PASS("(Enabled-checks) Test passed\n");
-			return;
-		}
-
-		FAIL("Expected EINVAL (%d) got %d\n", -EINVAL, err);
-	}
-
-	/* We have bypassed runtime checks of user_data. L2CAP will take our
-	 * `buf` with non-null user_data. We verify that:
+	/* L2CAP will take our `buf` with non-null user_data. We verify that:
 	 * - it is cleared
 	 * - we don't segfault later (e.g. in `tx_notify`)
 	 */

tests/bsim/bluetooth/host/l2cap/userdata/src/main_l2cap_userdata.c

@@ -8,6 +8,5 @@ INCR_BUILD=1
 source ${ZEPHYR_BASE}/tests/bsim/compile.source
 
 app="$(guess_test_relpath)" compile
-app="$(guess_test_relpath)" conf_file=prj_no_checks.conf compile
 
 wait_for_background_jobs

tests/bsim/bluetooth/host/l2cap/userdata/tests_scripts/_compile.sh

@@ -20,14 +20,3 @@ Execute ./bs_2G4_phy_v1 -v=${verbosity_level} -s=${simulation_id} \
     -D=2 -sim_length=5e6 $@
 
 wait_for_background_jobs
-
-Execute ./bs_${BOARD_TS}_tests_bsim_bluetooth_host_l2cap_userdata_prj_no_checks_conf \
-    -v=${verbosity_level} -s=${simulation_id} -d=0 -testid=central
-
-Execute ./bs_${BOARD_TS}_tests_bsim_bluetooth_host_l2cap_userdata_prj_no_checks_conf \
-    -v=${verbosity_level} -s=${simulation_id} -d=1 -testid=peripheral
-
-Execute ./bs_2G4_phy_v1 -v=${verbosity_level} -s=${simulation_id} \
-    -D=2 -sim_length=5e6 $@
-
-wait_for_background_jobs