Rule gains metric: u32 field (default 0). Lower metric = higher
priority. lookup_rule() now selects the matching rule with the
lowest metric among those with the same prefix length.
route/add parser accepts 'metric N':
default via 10.0.2.2 metric 100
default via 10.0.2.254 metric 200
Display shows metric when non-zero:
default via 10.0.2.2 dev eth0 src 10.0.2.15 metric 100
Rule::with_metric(m) builder added. All existing callers use
default metric=0 (backward compatible).
Use case: multi-homed hosts with primary/backup default routes.
The primary route has metric 0, the backup has metric 100.
All 31 tests pass.
Red Bear OS
e818909712