netxen: fix context deletion sequence

o Use D3 reset context deletion for NX2031, it cleans up
  more resources in the firmware.
o Release rx buffers after hardware context has been reset.
o Delete tx context after rx context, some firmware control
  commands are sent on tx context, so it should be the last
  to go.

Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: David S. Miller <davem@davemloft.net>