loader.efi: Retain standalone network configuration

DHCP initmd discovery used net_configure() to open and configure SNP,
then immediately closed the socket and released the protocol.
Selecting net0 as currdev subsequently required another exclusive
SNP attach, which may hang on some EDK II firmware.

Keep the configured socket available for ordinary network consumers
so NFS boot can reuse it. Add an explicit deconfiguration operation
and invoke it only when an initmd URL requires handing SNP back
to the firmware network stack.

Signed-off-by: Krzysztof Galazka <[email protected]>

Reviewed by:	imp
Assisted by:    Github Copilot (GPT-5.6 Sol)
Sponsored by:   Intel Corporation
Differential Revision:	https://reviews.freebsd.org/D59999

stand/common/dev_net.c

@@ -176,21 +176,42 @@ net_open(struct open_file *f, ...)
 int
 net_configure(struct devdesc *dev)
 {
-	int error, sock;
+	int error;
 
-	sock = netif_open(dev);
-	if (sock < 0)
+	if (netdev_sock >= 0)
+		return (0);
+
+	netdev_sock = netif_open(dev);
+	if (netdev_sock < 0)
 		return (ENXIO);
 
 	error = 0;
 	if (rootip.s_addr == 0)
-		error = net_getparams(sock);
+		error = net_getparams(netdev_sock);
 	if (error == 0)
-		net_setparams(sock);
-	netif_close(sock);
+		net_setparams(netdev_sock);
+	if (error != 0) {
+		netif_close(netdev_sock);
+		netdev_sock = -1;
+		return (error);
+	}
+
+	netdev_name = strdup(dev->d_dev->dv_name);
+	if (netdev_name == NULL) {
+		netif_close(netdev_sock);
+		netdev_sock = -1;
+		return (ENOMEM);
+	}
 	return (error);
 }
 
+void
+net_deconfigure(void)
+{
+
+	net_cleanup();
+}
+
 static int
 net_close(struct open_file *f)
 {

stand/common/dev_net.h

@@ -30,6 +30,7 @@
 extern struct devsw netdev;
 
 int net_configure(struct devdesc *);
+void net_deconfigure(void);
 uint32_t net_parse_rootpath(void);
 
 #endif

stand/efi/loader/memdisk.c

@@ -245,6 +245,8 @@ maybe_download_initmd(void)
 	if (url == NULL || *url == '\0')
 		return;
 
+	/* Release SNP so the firmware network stack can fetch the image. */
+	net_deconfigure();
 	printf("Downloading initmd from %s\n", url);
 	error = download_md_image(url);
 	if (error != 0 && error != ECANCELED)