canbus: isotp: convert SF length check from ASSERT to runtime check

Convert the ISO-TP SF length check in send_sf() from __ASSERT() to a
runtime check.

Fixes: #61501

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>
(cherry picked from commit 1b3d1e01deff942ef84cb08e9fa9b4c5e18de385)

subsys/canbus/isotp/isotp.c

diff --git a/subsys/canbus/isotp/isotp.c b/subsys/canbus/isotp/isotp.c
index 58918a0..5cc2b56 100644
--- a/subsys/canbus/isotp/isotp.c
+++ b/subsys/canbus/isotp/isotp.c
@@ -907,7 +907,11 @@
 
 	frame.data[index++] = ISOTP_PCI_TYPE_SF | len;
 
-	__ASSERT_NO_MSG(len <= ISOTP_CAN_DL - index);
+	if (len > ISOTP_CAN_DL - index) {
+		LOG_ERR("SF len does not fit DL");
+		return -ENOSPC;
+	}
+
 	memcpy(&frame.data[index], data, len);
 
 #ifdef CONFIG_ISOTP_ENABLE_TX_PADDING