linuxulator: map IFF_LOWER_UP through NETLINK_ROUTE for Linux apps

rtnl_if_flags_to_linux() translated the usual IFF_* bits but dropped
FreeBSD's IFF_LOWER_UP (IFF_NETLINK_1).  Chromium's AddressTrackerLinux
only treats a link as online when ifi_flags has UP|LOWER_UP|RUNNING; with
LOWER_UP missing, online_links stays empty, ConnectionType is
CONNECTION_NONE, and navigator.onLine is false even though TCP/HTTPS
work.  Linux Chromium under the Linuxulator (e.g. www/linux-brave) then
shows a spurious Offline UI; sites that ignore navigator.onLine do not.
Native www/chromium is on a different notifier path.

Map IFF_LOWER_UP to Linux's IFF_LOWER_UP (1<<16) and define
LINUX_IFF_LOWER_UP alongside the existing LINUX_IFF_* constants.

PR:	297424

Reviewed by:	pouria, adrian (previous revision)
Differential Revision:	https://reviews.freebsd.org/D58774

2 files changed, 7 insertions, 1 deletions

diff --git a/sys/compat/linux/linux.h b/sys/compat/linux/linux.h
index a9f753cd55b7..0c46860a6b36 100644
--- a/sys/compat/linux/linux.h
+++ b/sys/compat/linux/linux.h
@@ -124,6 +124,9 @@ struct l_sockaddr {
 #define	LINUX_IFF_PORTSEL	0x2000
 #define	LINUX_IFF_AUTOMEDIA	0x4000
 #define	LINUX_IFF_DYNAMIC	0x8000
+/* Volatile (netlink / ifinfomsg); not representable in ifr_flags short */
+#define	LINUX_IFF_LOWER_UP	0x10000
+#define	LINUX_IFF_DORMANT	0x20000
 
 /* sigaltstack */
 #define	LINUX_SS_ONSTACK	1
diff --git a/sys/compat/linux/linux_netlink.c b/sys/compat/linux/linux_netlink.c
index 256f188385ce..8c1659cb1dd8 100644
--- a/sys/compat/linux/linux_netlink.c
+++ b/sys/compat/linux/linux_netlink.c
@@ -342,8 +342,11 @@ rtnl_if_flags_to_linux(unsigned int if_flags)
 		case IFF_DYING:
 			/* No Linux analogue */
 			break;
+		case IFF_LOWER_UP:	/* IFF_NETLINK_1 */
+			result |= LINUX_IFF_LOWER_UP;
+			break;
 		case IFF_MULTICAST:
-			result |= 1 << 12;
+			result |= LINUX_IFF_MULTICAST;
 		}
 	}
 	return (result);