remove header name buffer

The header name buffer and its max length handling has actually
been unused since the minilex parser was introduced.  We hold
parsing state in the lex-type parts and don't need to store or
worry about max length, since the parser will let us know as
soon as it can't be a match for the valid header names.

This strips it out reducing the per-connection allocation for
x86_64 with default configure from 224 to 160.

Signed-off-by: Andy Green <andy.green@linaro.org>
remove current_alloc_len

Signed-off-by: Andy Green <andy.green@linaro.org>
minor type optimizations

Signed-off-by: Andy Green <andy.green@linaro.org>
migrate client hs and c_port into ah

Signed-off-by: Andy Green <andy.green@linaro.org>
fix no extensions build

Signed-off-by: Andy Green <andy.green@linaro.org>