[efi] Record cached ProxyDHCPOFFER and PXEBSACK, if present

Commit cd3de55 ("[efi] Record cached DHCPACK from loaded image's
device handle, if present") added the ability for a chainloaded UEFI
iPXE to reuse an IPv4 address and DHCP options previously obtained by
a built-in PXE stack, without needing to perform a second DHCP
request.

Extend this to also record the cached ProxyDHCPOFFER and PXEBSACK
obtained from the EFI_PXE_BASE_CODE_PROTOCOL instance installed on the
loaded image's device handle, if present.

This allows a chainloaded UEFI iPXE to reuse a boot filename or other
options that were provided via a ProxyDHCP or PXE boot server
mechanism, rather than by standard DHCP.

Tested-by: Andreas Hammarskjöld <junior@2PintSoftware.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/cachedhcp.h

@@ -12,6 +12,13 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <stddef.h>
 #include <ipxe/uaccess.h>
 
-extern int cachedhcp_record ( userptr_t data, size_t max_len );
+struct cached_dhcp_packet;
+
+extern struct cached_dhcp_packet cached_dhcpack;
+extern struct cached_dhcp_packet cached_proxydhcp;
+extern struct cached_dhcp_packet cached_pxebs;
+
+extern int cachedhcp_record ( struct cached_dhcp_packet *cache, userptr_t data,
+			      size_t max_len );
 
 #endif /* _IPXE_CACHEDHCP_H */

src/include/ipxe/dhcppkt.h

@@ -56,7 +56,7 @@ dhcppkt_put ( struct dhcp_packet *dhcppkt ) {
  * @v dhcppkt		DHCP packet
  * @ret len		Used length
  */
-static inline int dhcppkt_len ( struct dhcp_packet *dhcppkt ) {
+static inline size_t dhcppkt_len ( struct dhcp_packet *dhcppkt ) {
 	return ( offsetof ( struct dhcphdr, options ) +
 		 dhcppkt->options.used_len );
 }