networkd: unbreak routing_policy_rule_compare_func()

!r is the same r == 0, so this was short-circuiting the comparison when
streq(a->iff, b->iff) or streq(a->off, b->off). Before the parent commit which
moved those comparisons to the end, this was short-circuiting quite a bit
of the comparison function.

(cherry picked from commit 314ed4f9)
(cherry picked from commit 19ac31c9)