vmxnet3: add support for out of order rx completion

Currently, vmxnet3 processes rx completions in-order i.e. no
out of order completion descriptor is expected. With UPT, if
hardware supports LRO, then hardware can report out of order
rx completions. This patch enhances vmxnet3 to add this support.
This supports gets effective only when the corresponding feature
bit is set.

Also, minor enhancements are done for performance.

Signed-off-by: Ronak Doshi <doshir@vmware.com>
Acked-by: Guolin Yang <gyang@vmware.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>