blancco-init: load xhci_pci so USB-C NICs work, report why a link fails

The initrd has no udev, so only modules init names get loaded, and
xhci_pci is a module in the Ubuntu kernel. USB 3 / USB-C ports were
therefore dead in the UEFI Blancco path and a Dell USB-C to RJ45 adapter
never appeared; init took the onboard e1000e port with no cable.

- modprobe xhci_pci and xhci_pci_renesas before the NIC drivers
- bring up interfaces inside the carrier wait too, since USB NICs
  enumerate seconds after onboard ports
- on no-link, print each interface's driver and the NIC/firmware/link
  kernel messages before dropping to a shell

Live kexec-initrd.img also now carries the NIC firmware set from the
Blancco 7.20 early cpio (rtl_nic, tigon, bnx2x, ...) under /lib/firmware.
The playbook build does not add it yet.

playbook/blancco-init.sh

@@ -35,7 +35,11 @@ echo "[1/5] Loading NIC drivers via modprobe (resolves deps automatically)..."
 # Throw the full common-NIC driver list at the wall. modprobe resolves the
 # deps from /lib/modules/$KVER/modules.dep (built by prepare-boot-tools).
 # Anything missing is silently ignored; whatever matches PCI IDs will bind.
+# USB host controllers first: xhci_pci is a module in the Ubuntu kernel
+# (CONFIG_USB_XHCI_PCI=m) and there is no udev here, so without this no
+# USB 3 / USB-C port works and USB-C to RJ45 adapters never appear.
 for drv in \
+    xhci_pci xhci_pci_renesas \
     mii libphy ptp \
     e1000 e1000e igb igc ixgbe ixgbevf i40e ice iavf \
     tg3 bnx2 bnx2x bnxt_en b44 \
@@ -91,6 +95,8 @@ for i in $(seq 1 30); do
     for n in /sys/class/net/*; do
         name="${n##*/}"
         case "$name" in lo|wl*) continue ;; esac
+        # USB NICs enumerate seconds after onboard ports: bring up late ones too
+        [ "$(cat "$n/operstate" 2>/dev/null)" = "down" ] && { ip link set "$name" up 2>/dev/null || ifconfig "$name" up 2>/dev/null || true; }
         [ "$(cat "$n/carrier" 2>/dev/null)" = "1" ] && CARRIER="$name" && break 2
     done
     sleep 1
@@ -100,8 +106,11 @@ echo ""
 if [ -z "$CARRIER" ]; then
     echo "ERROR: no wired interface has link. Interfaces seen:"
     for n in /sys/class/net/*; do
-        echo "  ${n##*/} carrier=$(cat "$n/carrier" 2>/dev/null)"
+        drv=$(readlink "$n/device/driver" 2>/dev/null)
+        echo "  ${n##*/} carrier=$(cat "$n/carrier" 2>/dev/null) driver=${drv##*/}"
     done
+    echo "=== kernel messages (NIC / firmware / link) ==="
+    dmesg | grep -i -E 'eth|enp|enx|r8152|r8169|e1000e|igc|cdc|firmware|link' | tail -20
     echo "Check the cable, then type 'exit' to reboot."
     exec /bin/sh
 fi