Add required hook functions to netboot boot script

Initramfs-tools boot scripts must provide hook functions (netboot_top,
netboot_premount, netboot_bottom) and mount wrappers (mount_top, mount_premount,
mount_bottom) for the init script to call them properly.

Without these, the init script doesn't recognize netboot as a valid boot method
and falls back to trying /dev/root, causing "cannot open block device" errors.

initramfs/scripts/netboot

@@ -7,6 +7,38 @@ export PATH=/usr/bin:/usr/sbin:/bin:/sbin
 MOUNTPOINT=/root
 TMPFS_MOUNT=/mnt
 
+# Hook functions for initramfs-tools boot script integration
+netboot_top()
+{
+	if [ "${netboot_top_used}" != "yes" ]; then
+		[ "${quiet?}" != "y" ] && log_begin_msg "Running /scripts/netboot-top"
+		run_scripts /scripts/netboot-top
+		[ "$quiet" != "y" ] && log_end_msg
+	fi
+	netboot_top_used=yes
+}
+
+netboot_premount()
+{
+	if [ "${netboot_premount_used}" != "yes" ]; then
+		[ "${quiet?}" != "y" ] && log_begin_msg "Running /scripts/netboot-premount"
+		run_scripts /scripts/netboot-premount
+		[ "$quiet" != "y" ] && log_end_msg
+	fi
+	netboot_premount_used=yes
+}
+
+netboot_bottom()
+{
+	if [ "${netboot_premount_used}" = "yes" ] || [ "${netboot_top_used}" = "yes" ]; then
+		[ "${quiet?}" != "y" ] && log_begin_msg "Running /scripts/netboot-bottom"
+		run_scripts /scripts/netboot-bottom
+		[ "$quiet" != "y" ] && log_end_msg
+	fi
+	netboot_premount_used=no
+	netboot_top_used=no
+}
+
 # Parse kernel command line for HTTP root
 parse_cmdline() {
     for x in $(cat /proc/cmdline); do
@@ -27,6 +59,11 @@ parse_cmdline() {
 
 mountroot() {
     rc=1
+
+    # Run hook scripts
+    netboot_top
+    netboot_premount
+
     parse_cmdline
 
     if test -z "${ROOT_URL}"; then
@@ -145,3 +182,19 @@ mountroot() {
 
     return ${rc}
 }
+
+# Standard mount hook wrappers expected by initramfs init
+mount_top()
+{
+	netboot_top
+}
+
+mount_premount()
+{
+	netboot_premount
+}
+
+mount_bottom()
+{
+	netboot_bottom
+}