OPTIM: tools: inline hex2i()

OPTIM: tools: inline hex2i()

This tiny function was not inlined because initially not much used.
However it's been used un the chunk parser for a while and it became
one of the most CPU-cycle eater there. By inlining it, the chunk parser
speed was increased by 74 %. We're almost 3 times faster than original
with just the last 4 commits.