efi_loader: Add network access support

We can now successfully boot EFI applications from disk, but users
may want to also run them from a PXE setup.

This patch implements rudimentary network support, allowing a payload
to send and receive network packets.

With this patch, I was able to successfully run grub2 with network
access inside of QEMU's -M xlnx-ep108.

Signed-off-by: Alexander Graf <agraf@suse.de>

net/tftp.c

@@ -8,6 +8,7 @@
 
 #include <common.h>
 #include <command.h>
+#include <efi_loader.h>
 #include <mapmem.h>
 #include <net.h>
 #include <net/tftp.h>
@@ -804,6 +805,7 @@ void tftp_start(enum proto_t protocol)
 		printf("Load address: 0x%lx\n", load_addr);
 		puts("Loading: *\b");
 		tftp_state = STATE_SEND_RRQ;
+		efi_set_bootdev("Net", "", tftp_filename);
 	}
 
 	time_start = get_timer(0);