net: statistics: Provide specific Kconfig options

This will help to track only what's wanted (ipv6, tpc, udp, else...) if
needed to.

Change-Id: I5c2e5e582db629b5d0e1cd98004f693c50f532a4
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>