selftests/net: enable fragments for fib-onlink-tests

We miss CONFIG_* fragments so test fib-onlink-tests.sh can do:
ip li add lisa type vrf table 1101
ip li add veth1 type veth peer name veth2

And the follow message occurs if it isn't enabled:
Configuring interfaces
RTNETLINK answers: Operation not supported

This enables for NET_NRF (and friends) and VETH so we can create a vrf
table and veth.

Fixes: 153e1b84 ("selftests: Add FIB onlink tests")
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>