ppp: allow usage in namespaces

Check for CAP_NET_ADMIN with ns_capable() instead of capable()
to allow usage of ppp in user namespace other than the init one.
Signed-off-by: NMatteo Croce <mcroce@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ppp/ppp_generic.c

@@ -390,7 +390,7 @@ static int ppp_open(struct inode *inode, struct file *file)
 	/*
 	 * This could (should?) be enforced by the permissions on /dev/ppp.
 	 */
-	if (!capable(CAP_NET_ADMIN))
+	if (!ns_capable(file->f_cred->user_ns, CAP_NET_ADMIN))
 		return -EPERM;
 	return 0;
 }