vlan: uninline __vlan_hwaccel_rx

The function is huge and included at least once in every VLAN acceleration
capable driver. Uninline it; to avoid having drivers depend on the VLAN
module, the function is always built in statically when VLAN is enabled.

With all VLAN acceleration capable drivers that build on x86_64 enabled,
this results in:

   text    data     bss     dec     hex filename
6515227  854044  343968 7713239  75b1d7 vmlinux.inlined
6505637  854044  343968 7703649  758c61 vmlinux.uninlined
----------------------------------------------------------
  -9590

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>