[efi] Add missing SANBOOT_PROTO_HTTP to EFI default configuration

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/defaults/efi.h

 #define	SANBOOT_PROTO_AOE	/* AoE protocol */
 #define	SANBOOT_PROTO_IB_SRP	/* Infiniband SCSI RDMA protocol */
 #define	SANBOOT_PROTO_FCP	/* Fibre Channel protocol */
+#define	SANBOOT_PROTO_HTTP	/* HTTP SAN protocol */
 
 #define	USB_HCD_XHCI		/* xHCI USB host controller */
 #define	USB_HCD_EHCI		/* EHCI USB host controller */