net: bcmasp: Keep buffers through power management

There is no advantage of freeing and re-allocating buffers through
suspend and resume. This waste cycles and makes suspend/resume time
longer. We also open ourselves to failed allocations in systems with
heavy memory fragmentation.

Signed-off-by: Justin Chen <justin.chen@broadcom.com>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>