CLEANUP: http: avoid duplicating literals in find_http_meth()

CLEANUP: http: avoid duplicating literals in find_http_meth()

The function does the inverse of http_known_methods[], better rely on
that array with its indices, that makes the code clearer. Note that
we purposely don't use a loop because the compiler is able to build
an evaluation tree of the size checks and content checks that's very
efficient for the most common methods. Moving a few unimportant
entries even simplified the output code a little bit (they're now
groupped by size without changing anything for the first ones).