MEDIUM: ist: always turn header names to lower case

HTTP/2 and above require header names to be lower cased, while HTTP/1
doesn't care. By making lower case the standard way to store header
names in HTX, we can significantly simplify all operations applying to
header names retrieved from HTX (including, but not limited to, lookups
and lower case checks which are not needed anymore).

As a side effect of replacing memcpy() with ist2bin_lc(), a small increase
of the request rate performance of about 0.5-1% was noticed on keep-alive
traffic, very likely due to memcpy() being overkill for tiny strings.

This trivial patch was marked medium because it may have a visible end-user
impact (e.g. non-HTTP compliant agent, etc).
1 file changed