fix(net): silence benign no-network warnings; add e1000e (82574) support

- smolnetd: an empty ip_router (DHCP-managed or deliberately network-less like
  the bare target) is a valid 'no default gateway' state, not a malformed config
  -> no warning.
- router: a limited/directed IPv4 broadcast (DHCP DISCOVER to 255.255.255.255
  before any lease/route exists) legitimately has no routing-table entry; don't
  warn 'No route found' for broadcast destinations.
- e1000d: add the 82574L (0x10d3, QEMU '-device e1000e') to the E1000 match
  list; it keeps the legacy descriptor/register interface this driver uses.
  I219 is intentionally excluded (integrated MDIO PHY, different init).

netstack/src/scheme/mod.rs

@@ -112,12 +112,18 @@ impl Smolnetd {
         // than panicking. The route lookup below will return None for
         // an invalid gateway, which is the correct degraded behavior.
         let default_gw = match getcfg("ip_router") {
+            Ok(s) if s.trim().is_empty() => {
+                // Empty ip_router is a valid "no default gateway" configuration
+                // (DHCP will fill it in, or the host is deliberately network-less
+                // like the bare target). Not a warning.
+                Ipv4Address::new(0, 0, 0, 0)
+            }
             Ok(s) => Ipv4Address::from_str(s.trim()).unwrap_or_else(|_| {
                 log::warn!("smolnetd: invalid ip_router '{}' in cfg, using 0.0.0.0", s);
                 Ipv4Address::new(0, 0, 0, 0)
             }),
-            Err(e) => {
-                log::warn!("smolnetd: ip_router not set in cfg ({:?}), using 0.0.0.0", e);
+            Err(_) => {
+                // File absent = no gateway configured; also a normal state.
                 Ipv4Address::new(0, 0, 0, 0)
             }
         };