net: fix packet socket delivery in rx irq handler

The changes to deliver hardware accelerated VLAN packets to packet
sockets (commit bc1d0411

) caused a warning for non-NAPI drivers.
The __vlan_hwaccel_rx() function is called directly from the drivers
RX function, for non-NAPI drivers that means its still in RX IRQ
context:

[   27.779463] ------------[ cut here ]------------
[   27.779509] WARNING: at kernel/softirq.c:136 local_bh_enable+0x37/0x81()
...
[   27.782520]  [<c0264755>] netif_nit_deliver+0x5b/0x75
[   27.782590]  [<c02bba83>] __vlan_hwaccel_rx+0x79/0x162
[   27.782664]  [<f8851c1d>] atl1_intr+0x9a9/0xa7c [atl1]
[   27.782738]  [<c0155b17>] handle_IRQ_event+0x23/0x51
[   27.782808]  [<c015692e>] handle_edge_irq+0xc2/0x102
[   27.782878]  [<c0105fd5>] do_IRQ+0x4d/0x64

Split hardware accelerated VLAN reception into two parts to fix this:

- __vlan_hwaccel_rx just stores the VLAN TCI and performs the VLAN
  device lookup, then calls netif_receive_skb()/netif_rx()

- vlan_hwaccel_do_receive(), which is invoked by netif_receive_skb()
  in softirq context, performs the real reception and delivery to
  packet sockets.

Reported-and-tested-by: Ramon Casellas <ramon.casellas@cttc.es>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>