i40e: Fix i40e_print_features() VEB mode output

Commit 7fd89545 ("i40e: remove BUG_ON from feature string building")
added defective output when I40E_FLAG_VEB_MODE_ENABLED was set in
function i40e_print_features.

Fix it.

Miscellanea:

- Remove unnecessary string variable
- Add space before not after fixed strings
- Use kmalloc not kzalloc
- Don't initialize i to 0, use result of first snprintf

Reported-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>