net: Getting rid of the x86 dependency to built vmxnet3

This patch removes config dependency on x86 to build vmxnet3 driver. Thus
the driver can be built on big endian architectures now. Although vmxnet3
is not supported on VMs other than x86 architecture, all this code goes in
to ensure correctness. If the code is not dependent on x86, it should not
assume little endian architecture in any of its operations.

Signed-off-by: Shreyas Bhatewara <sbhatewara@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>