vmxnet3: Update driver to use ethtool_sprintf

So this patch actually does 3 things.

First it removes a stray white space at the start of the variable
declaration in vmxnet3_get_strings.

Second it flips the logic for the string test so that we exit immediately
if we are not looking for the stats strings. Doing this we can avoid
unnecessary indentation and line wrapping.

Then finally it updates the code to use ethtool_sprintf rather than a
memcpy and pointer increment to write the ethtool strings.

Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>