Re-enable loader efi http boot and fix dv_open bug if dv_init failed

The code in efihttp.c was assuming that dv_open wouldn't be called if
dv_init failed. But the dv_init return value is currently ignored.

Add a new variable, `efihttp_init_done` and only proceed in dv_open if
it's true. This fixes the loader on systems without efi http support.

stand/efi/libefi/efihttp.c

@@ -52,6 +52,8 @@ static EFI_GUID http_guid = EFI_HTTP_PROTOCOL_GUID;
 static EFI_GUID httpsb_guid = EFI_HTTP_SERVICE_BINDING_PROTOCOL_GUID;
 static EFI_GUID ip4config2_guid = EFI_IP4_CONFIG2_PROTOCOL_GUID;
 
+static bool efihttp_init_done = false;
+
 static int efihttp_dev_init(void);
 static int efihttp_dev_strategy(void *devdata, int rw, daddr_t blk, size_t size,
     char *buf, size_t *rsize);
@@ -208,6 +210,9 @@ efihttp_dev_init(void)
 		return (efi_status_to_errno(status));
 
 	err = efi_register_handles(&efihttp_dev, &handle, NULL, 1);
+	if (!err)
+		efihttp_init_done = true;
+
 	return (err);
 }
 
@@ -236,6 +241,9 @@ efihttp_dev_open(struct open_file *f, ...)
 	EFI_STATUS status;
 	int err, len;
 
+	if (!efihttp_init_done)
+		return (ENXIO);
+
 	imgpath = efi_lookup_image_devpath(IH);
 	if (imgpath == NULL)
 		return (ENXIO);
@@ -555,6 +563,8 @@ efihttp_fs_open(const char *path, struct open_file *f)
 	char *path_slash;
 	int err;
 
+	if (!efihttp_init_done)
+		return (ENXIO);
 	/*
 	 * If any path fails to open, try with a trailing slash in
 	 * case it's a directory.

stand/efi/loader/conf.c

@@ -39,6 +39,7 @@ struct devsw *devsw[] = {
 	&efipart_fddev,
 	&efipart_cddev,
 	&efipart_hddev,
+	&efihttp_dev, /* ordering with efinet_dev matters */
 	&efinet_dev,
 	&vdisk_dev,
 #ifdef EFI_ZFS_BOOT
@@ -54,6 +55,7 @@ struct fs_ops *file_system[] = {
 	&dosfs_fsops,
 	&ufs_fsops,
 	&cd9660_fsops,
+	&efihttp_fsops,
 	&tftp_fsops,
 	&nfs_fsops,
 	&gzipfs_fsops,