ppp: Remove redundant BUG_ON() check in ppp_pernet

Passing NULL to ppp_pernet causes a crash via BUG_ON.
Dereferencing net in net_generic() also has the same effect.
This patch removes the redundant BUG_ON check on the same parameter.
Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ppp/ppp_generic.c

@@ -296,8 +296,6 @@ static struct class *ppp_class;
 /* per net-namespace data */
 static inline struct ppp_net *ppp_pernet(struct net *net)
 {
-	BUG_ON(!net);
-
 	return net_generic(net, ppp_net_id);
 }