With ISO 15765-2:2016 the PDU size is not limited to 2^12 - 1 (4095)
bytes but can be represented as a 32 bit unsigned integer value which
allows 2^32 - 1 bytes (~4GB). The use-cases like automotive unified
diagnostic services (UDS) and flashing of ECUs still use the small
static buffers which are provided at socket creation time.

When a use-case requires to transfer PDUs up to 1025 kByte the maximum
PDU size can now be extended by setting the module parameter
max_pdu_size. The extended size buffers are only allocated on a
per-socket/connection base when needed at run-time.

changes since v2: https://lore.kernel.org/all/20230313172510.3851-1-socketcan@hartkopp.net
- use ARRAY_SIZE() to reference DEFAULT_MAX_PDU_SIZE only at one place

changes since v1: https://lore.kernel.org/all/20230311143446.3183-1-socketcan@hartkopp.net
- limit the minimum 'max_pdu_size' to 4095 to maintain the classic
  behavior before ISO 15765-2:2016

Link: https://github.com/raspberrypi/linux/issues/5371Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20230326115911.15094-1-socketcan@hartkopp.netSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>