NetServices: implement support for HEAD requests and 204 responses.

These particular responses will not have a body. This is now handled by the
BHttpSession object. There is also a minor fix in here that prevents a crash
when multiple requests are handled by the DataThread at the same time, and not
all of the requests have events.

Change-Id: I7f47d8b3cd8491c8193275be4b3fc1080780fa20

headers/private/netservices2/HttpRequest.h

@@ -59,6 +59,9 @@ public:
 			BHttpMethod&		operator=(const BHttpMethod& other);
 			BHttpMethod&		operator=(BHttpMethod&& other) noexcept;
 
+	// Comparison
+			bool				operator==(const Verb& other) const noexcept;
+
 	// Get the method as a string
 	const	std::string_view	Method() const noexcept;