net: cgroups: fix build errors when linux/phy*.h is removed from net/dsa.h

net/core/netprio_cgroup.c:303:16: error: expected declaration specifiers or '...' before string constant
    MODULE_LICENSE("GPL v2");
                   ^~~~~~~~

Add linux/module.h to fix this.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>