bpf: fix splat for illegal devmap percpu allocation

It was reported that syzkaller was able to trigger a splat on
devmap percpu allocation due to illegal/unsupported allocation
request size passed to __alloc_percpu():

  [   70.094249] illegal size (32776) or align (8) for percpu allocation
  [   70.094256] ------------[ cut here ]------------
  [   70.094259] WARNING: CPU: 3 PID: 3451 at mm/percpu.c:1365 pcpu_alloc+0x96/0x630
  [...]
  [   70.094325] Call Trace:
  [   70.094328]  __alloc_percpu_gfp+0x12/0x20
  [   70.094330]  dev_map_alloc+0x134/0x1e0
  [   70.094331]  SyS_bpf+0x9bc/0x1610
  [   70.094333]  ? selinux_task_setrlimit+0x5a/0x60
  [   70.094334]  ? security_task_setrlimit+0x43/0x60
  [   70.094336]  entry_SYSCALL_64_fastpath+0x1a/0xa5

This was due to too large max_entries for the map such that we
surpassed the upper limit of PCPU_MIN_UNIT_SIZE. It's fine to
fail naturally here, so switch to __alloc_percpu_gfp() and pass
__GFP_NOWARN instead.

Fixes: 11393cc9 ("xdp: Add batching support to redirect map")
Reported-by: Mark Rutland <mark.rutland@arm.com>
Reported-by: Shankara Pailoor <sp3485@columbia.edu>
Reported-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>