include: net: http: rename http_x.h http/x.h

Some minor housekeeping prior to adding an http server
implementation. There are already a number of http headers
and that number will likely increase with subsequent work.
Moving them into a common directory cleans up the
`include/net` directory a bit.

Signed-off-by: Christopher Friedt <cfriedt@meta.com>

subsys/net/lib/http/http_client.c

@@ -22,7 +22,7 @@ LOG_MODULE_REGISTER(net_http, CONFIG_NET_HTTP_LOG_LEVEL);
 
 #include <zephyr/net/net_ip.h>
 #include <zephyr/net/socket.h>
-#include <zephyr/net/http_client.h>
+#include <zephyr/net/http/client.h>
 
 #include "net_private.h"
 

subsys/net/lib/http/http_parser.c

@@ -23,7 +23,7 @@
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  * IN THE SOFTWARE.
  */
-#include <zephyr/net/http_parser.h>
+#include <zephyr/net/http/parser.h>
 #include <zephyr/sys/__assert.h>
 #include <stddef.h>
 #include <ctype.h>

subsys/net/lib/http/http_parser_url.c

@@ -29,7 +29,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <limits.h>
-#include <zephyr/net/http_parser_url.h>
+#include <zephyr/net/http/parser_url.h>
 #include <zephyr/toolchain.h>
 
 #ifndef BIT_AT