Upstream will be removing the incorrect TUN_* flags from if_tun.h so we might as well use the replacements.  Technically TUN_TYPE_MASK and TUN_TUN_DEV/TUN_TAP_DEV were not incorrect as they have the same value as their IFF_* replacements, but they're considered deprecated too.

diff --git a/src/platform/nm-linux-platform.c b/src/platform/nm-linux-platform.c
index 42444d9..391f175 100644
--- a/src/platform/nm-linux-platform.c
+++ b/src/platform/nm-linux-platform.c
@@ -2964,7 +2964,7 @@ tun_get_properties (NMPlatform *platform, int ifindex, NMPlatformTunProperties *
 #ifndef IFF_MULTI_QUEUE
                        const int IFF_MULTI_QUEUE = 0x0100;
 #endif
-                       props->mode = ((flags & TUN_TYPE_MASK) == TUN_TUN_DEV) ? "tun" : "tap";
+                       props->mode = ((flags & (IFF_TUN | IFF_TAP)) == IFF_TUN) ? "tun" : "tap";
                        props->no_pi = !!(flags & IFF_NO_PI);
                        props->vnet_hdr = !!(flags & IFF_VNET_HDR);
                        props->multi_queue = !!(flags & IFF_MULTI_QUEUE);