net/usb/r8152: support aggregation

Enable the tx/rx aggregation which could contain one or more packets
for each bulk in/out. This could reduce the loading of the host
controller by sending less bulk transfer.

The rx packets in the bulk in buffer should be 8-byte aligned, and
the tx packets in the bulk out buffer should be 4-byte aligned.

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>