benet: use GFP_KERNEL allocations when possible

Extend be_alloc_pages() with a gfp parameter, so that we use GFP_KERNEL
allocations instead of GFP_ATOMIC when not running in softirq context.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Ajit Khaparde <ajit.khaparde@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>