int16 blobmsg type is currently being serialized as uint16_t due to
missing cast during JSON output.
Following blobmsg content:
bar-min: -32768 (i16)
bar-max: 32767 (i16)
Produces following JSON:
{ "bar-min":32768,"bar-max":32767 }
Whereas one would expect:
{ "bar-min":-32768,"bar-max":32767 }
Reviewed-by: Jo-Philipp Wich <jo@mein.io>
Signed-off-by: Petr Štetiar <ynezz@true.cz>