include/net/netprio_cgroup.h: various fixes

include/net/netprio_cgroup.h: various fixes

- make task_netprio_state() stub an inline C function

- Untangle strange ifdef arrangement - remove mention of CONFIG_CGROUPS
  and make everything depend on CONFIG_NETPRIO_CGROUP.

- Don't build sock_update_netprioidx() when CONFIG_NETPRIO_CGROUP=n

- make the skb_update_prio() stub an inlined C function

Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: John Fastabend <john.r.fastabend@intel.com>
Cc: Robert Love <robert.w.love@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>