include: add reserved field for #926
include: add reserved field for #926

Introduce reserved field to be able to fix #926 after v0.12 release.

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso