[gupnp] linux-cm: Fix compiling if wireless.h is missing

[Jens Georg <jensgeorg src gnome org>]

commit 8416ad5d112eef9eff2c1eb0c4450a1ef003912f
Author: Jens Georg <mail jensge org>
Date:   Thu Nov 29 12:33:08 2018 +0100

    linux-cm: Fix compiling if wireless.h is missing

 libgupnp/gupnp-linux-context-manager.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/libgupnp/gupnp-linux-context-manager.c b/libgupnp/gupnp-linux-context-manager.c
index 563c0c9..000e469 100644
--- a/libgupnp/gupnp-linux-context-manager.c
+++ b/libgupnp/gupnp-linux-context-manager.c
@@ -47,6 +47,7 @@
 #include <sys/socket.h>
 #include <linux/netlink.h>
 #include <linux/rtnetlink.h>
+#include <net/if.h>
 #ifdef HAVE_LINUX_WIRELESS_H
 #include <linux/wireless.h>
 #endif