nfp: bpf: allow disabling TC offloads when XDP active

TC BPF offload was added first, so we used to assume that
the ethtool TC HW offload flag cannot be touched whenever
any BPF program is loaded on the NIC.  This unncessarily
limits changes to the TC flag when offloaded program is XDP.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>