kernel-install: ignore extra args passed when invoked as installkernel

kernel's 'make install' invokes install.sh which calls /sbin/install-kernel.
Thus we are invoked as e.g.
  /sbin/installkernel 5.18.0 arch/x86/boot/bzImage System.map /boot
The last two arguments would be passed as "initrds".

Before , we would just quitely ignore
/boot, because it doesn't pass the 'test -f' test, and possibly try to do
something with System.map. 742561e tightened
the check, so we now throw an error.

It seems that the correct thing is to ignore those two arguments, because
our plugin syntax has no notion of System.map. And the installation directory
we can figure out ourselves better. Effectively, this makes things behave
like before, but less by accident.

Fixes #23490.

src/kernel-install/kernel-install.in

@@ -81,9 +81,11 @@ fi
 if [ "${0##*/}" = "installkernel" ]; then
     COMMAND=add
     # make install doesn't pass any initrds
+    no_initrds=1
 else
     COMMAND="$1"
     [ $# -ge 1 ] && shift
+    no_initrds=0
 fi
 
 if [ "$COMMAND" = "inspect" ]; then
@@ -321,8 +323,17 @@ case "$COMMAND" in
         fi
 
         for f in $PLUGINS; do
-            [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ] && echo "+$f add $KERNEL_VERSION $ENTRY_DIR_ABS $*"
-            "$f" add "$KERNEL_VERSION" "$ENTRY_DIR_ABS" "$@"
+            if [ "$no_initrds" = 1 ]; then
+                # kernel's install.sh invokes us as
+                #   /sbin/installkernel <version> <vmlinuz> <map> <installation-dir>
+                # We ignore the last two arguments.
+                [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ] && echo "+$f add $KERNEL_VERSION $ENTRY_DIR_ABS $1"
+                "$f" add "$KERNEL_VERSION" "$ENTRY_DIR_ABS" "$1"
+            else
+                [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ] && echo "+$f add $KERNEL_VERSION $ENTRY_DIR_ABS $*"
+                "$f" add "$KERNEL_VERSION" "$ENTRY_DIR_ABS" "$@"
+            fi
+
             err=$?
             [ $err -eq $skip_remaining ] && break
             ret=$(( ret + err ))