net/netif_receive_skb_core: Use migrate_disable()

The preempt disable around do_xdp_generic() has been introduced in
commit
   bbbe211c ("net: rcu lock and preempt disable missing around generic xdp")

For BPF it is enough to use migrate_disable() and the code was updated
as it can be seen in commit
   3c58482a

 ("bpf: Provide bpf_prog_run_pin_on_cpu() helper")

This is a leftover which was not converted.

Use migrate_disable() before invoking do_xdp_generic().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>