zebra: Don't bother ref'ing ifp in zebra_pbr_rule

zebra: Don't bother ref'ing ifp in zebra_pbr_rule

If we only really use the ifp for the name, then
don't bother referencing the ifp. If that ifp is
freed, we don't expect zebra to handle the rules that
use it (that's pbrd's job), so it is going to be
pointing to unintialized memory when we decide to remove
that rule later. Thus, just keep the name in the data
and dont mess with pointer refs.

Signed-off-by: Stephen Worley <sworley@cumulusnetworks.com>