webdav/frontend: fix IllegalArgumentException "not an IP string literal"

Motivation:

Commit 8e4d90e merged commit c0e8abf from dependabot[bot]
<support@github.com> that resolves a security vulnerability by bumping
the Jetty version from 9.4.18.v20190429 to 9.4.34.v20201102.

This new version of Jetty resolves issue jetty/jetty.project#5079,
with the effect that HttpServletRequest#getRemoteAddr now returns IPv6
addresses in square brackets.  Previously, the getRemoteAddr method
returned IPv6 addresses without square brackets.

The result of this change in format means that calling Guava's
InetAddresses.forString now throws an IllegalArgumentException if
dCache's WebDAV or frontend is used with an IPv6 address.

Modification:

Update Guava usage to a method that expects IPv6 addresses in square
brackets.

Result:

dCache WebDAV and frontend now work with IPv6 interfaces.

Target: master
Requires-notes: no
Requires-book: no
Patch: https://rb.dcache.org/r/12671/
Acked-by: Tigran Mkrtchyan
Acked-by: Lea Morschel

modules/dcache/src/main/java/org/dcache/http/AbstractLoggingHandler.java

@@ -87,7 +87,7 @@ protected void describeOperation(NetLoggerBuilder log,
         log.add("response.code", response.getStatus());
         log.add("response.reason", getReason(response));
         log.add("location", response.getHeader("Location"));
-        InetAddress addr = InetAddresses.forString(request.getRemoteAddr());
+        InetAddress addr = InetAddresses.forUriString(request.getRemoteAddr());
         log.add("socket.remote", new InetSocketAddress(addr, request.getRemotePort()));
         log.add("user-agent", request.getHeader("User-Agent"));