Header limit of 32 KiB, upstream URL checks, build and run scripts

The request line and headers are now refused above 32 KiB exactly: Go's
server reads 4 KiB past MaxHeaderBytes, so that is set to 28 KiB, and
the tests try exactly 32 KiB and one byte more. SWWAF_UPSTREAM_URL now
needs a host, and a given port must be from 1 to 65535. make build and
make run call script/build and script/run.

Model: opus-5-5

SPEC.md

@@ -442,8 +442,7 @@ The settings, by group:
       longer than `SWWAF_CLIENT_REQUEST_TIMEOUT` to send them gets no answer:
       the server closes its connection. Headers over
       `SWWAF_CLIENT_REQUEST_HEADER_MAX_BYTES` are answered `431` by the server
-      itself, which reads up to 4 KiB past the limit before it refuses. Neither
-      request gets a line in the request log.
+      itself. Neither request gets a line in the request log.
     - A WebSocket connection leaves these limits behind once it is upgraded: it
       stays open until either side closes it.
 - Lookup of AS number and country (R7). On by default through GeoJS, which needs