net: Get pxe config file from dhcp option 209

Allow dhcp server pass pxe config file full path by using option 209

Signed-off-by: Sean Edmond <seanedmond@microsoft.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index fd16c3a..df6d71c 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1840,6 +1840,10 @@
 	default 0x15 if ARM
 	default 0x0 if X86
 
+config BOOTP_PXE_DHCP_OPTION
+	bool "Request & store 'pxe_configfile' from BOOTP/DHCP server"
+	depends on BOOTP_PXE
+
 config BOOTP_VCI_STRING
 	string
 	depends on CMD_BOOTP
diff --git a/cmd/pxe.c b/cmd/pxe.c
index 7045897..21134eb 100644
--- a/cmd/pxe.c
+++ b/cmd/pxe.c
@@ -141,6 +141,14 @@
 			  env_get("bootfile"), use_ipv6))
 		return -ENOMEM;
 
+	if (IS_ENABLED(CONFIG_BOOTP_PXE_DHCP_OPTION) &&
+	    pxelinux_configfile && !use_ipv6) {
+		if (pxe_dhcp_option_path(&ctx, pxefile_addr_r) > 0)
+			goto done;
+
+		goto error_exit;
+	}
+
 	if (IS_ENABLED(CONFIG_DHCP6_PXE_DHCP_OPTION) &&
 	    pxelinux_configfile && use_ipv6) {
 		if (pxe_dhcp_option_path(&ctx, pxefile_addr_r) > 0)