net/vmxnet3: increase Rx data ring descriptor size

net/vmxnet3: increase Rx data ring descriptor size

Vmxnet3 driver supports receive data ring viz. a set of small sized
buffers that are always mapped by the emulation. If a packet fits into
the receive data ring buffer, the emulation delivers the packet via the
receive data ring.

Increasing the receive data ring descriptor size from 128 to 256
showed performance gains as high as 5% for packets smaller than 256.

Signed-off-by: Shraddha Joshi <jshraddha@vmware.com>
Acked-by: Jin Heo <heoj@vmware.com>
Acked-by: Guolin Yang <gyang@vmware.com>
Acked-by: Boon Ang <bang@vmware.com>
Acked-by: Yong Wang <yongwang@vmware.com>