can-isotp: add SF_BROADCAST support for functional addressing

When CAN_ISOTP_SF_BROADCAST is set in the CAN_ISOTP_OPTS flags the CAN_ISOTP socket is switched into functional addressing mode, where only single frame (SF) protocol data units can be send on the specified CAN interface and the given tp.tx_id after bind().

In opposite to normal and extended addressing this socket does not register a CAN-ID for reception which would be needed for a 1-to-1 ISOTP connection with a segmented bi-directional data transfer.

Sending SFs on this socket is therefore a TX-only 'broadcast' operation.

---
 include/uapi/linux/can/isotp.h |  2 +-
 net/can/isotp.c                | 42 +++++++++++++++++++++++-----------
 2 files changed, 30 insertions(+), 14 deletions(-)

index 7793b26aa154..c55935b64ccc 100644
@@ -133,11 +133,11 @@ struct can_isotp_ll_options {
 #define CAN_ISOTP_HALF_DUPLEX	0x040	/* half duplex error state handling */
 #define CAN_ISOTP_FORCE_TXSTMIN	0x080	/* ignore stmin from received FC */
 #define CAN_ISOTP_FORCE_RXSTMIN	0x100	/* ignore CFs depending on rx stmin */
 #define CAN_ISOTP_RX_EXT_ADDR	0x200	/* different rx extended addressing */
 #define CAN_ISOTP_WAIT_TX_DONE	0x400	/* wait for tx completion */
-
+#define CAN_ISOTP_SF_BROADCAST	0x800	/* 1-to-N functional addressing */
 
 /* default values */
 
 #define CAN_ISOTP_DEFAULT_FLAGS		0
 #define CAN_ISOTP_DEFAULT_EXT_ADDRESS	0x00

2.29.2