Fix intermittent RadioLib static SPI buffer overflow
When RADIOLIB_STATIC_ONLY=1 is set, RadioLib's SPItransferStream()
allocates two fixed-size stack buffers (buffOut and buffIn) of
RADIOLIB_STATIC_ARRAY_SIZE bytes each, instead of heap-allocating
exactly the right size.
The default value of RADIOLIB_STATIC_ARRAY_SIZE is 256. When receiving
a maximum-size LoRa packet (255 bytes, equal to MAX_TRANS_UNIT),
SX126x::readBuffer() passes a 3-byte SPI command header
(CMD_READ_BUFFER + offset + NOP) plus 255 bytes of payload to
SPItransferStream(), for a total buffLen of 258 bytes. This overflows
the 256-byte stack buffers by 2 bytes, corrupting adjacent locals and
occasionally the stack canary, triggering __stack_chk_fail.
The same overflow occurs on the transmit path: SX126x::writeBuffer()
passes a 2-byte command header plus 255 bytes of payload (buffLen=257),
also overflowing the 256-byte buffer.
The overflow is small (2 bytes on the read path, 1 byte on the write
path), so it only intermittently reaches the stack canary depending on
compiler-generated stack frame layout.
Set RADIOLIB_STATIC_ARRAY_SIZE=260 to eliminate the overflow on both
paths, with 2 bytes of margin on the read path (258 < 260) and 3 bytes
on the write path (257 < 260). The value is placed in [arduino_base] so
it applies to all target platforms.
Valentin V. Bartenev