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 <[e-mail]>

drivers/net/wireless/mac80211_hwsim.c

···
 	cp->magic = 0;
 }
 
-static unsigned int hwsim_net_id;
+static int hwsim_net_id;
 
 static int hwsim_netgroup;