mac80211_hwsim: use signed net namespace ID

The API expects a pointer to a signed int so we should not use an
unsigned int for it.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/drivers/net/wireless/mac80211_hwsim.c b/drivers/net/wireless/mac80211_hwsim.c
index 97196c4..337794f 100644
--- a/drivers/net/wireless/mac80211_hwsim.c
+++ b/drivers/net/wireless/mac80211_hwsim.c
@@ -250,7 +250,7 @@
 	cp->magic = 0;
 }
 
-static unsigned int hwsim_net_id;
+static int hwsim_net_id;
 
 static int hwsim_netgroup;