build initramfs: unclear _mpargs in instmods()

The local variable _mpargs in function instmods() in file dracut-functions
looks peculiar.  The documentation is non-existent, but still ...

First, $_mpargs is not passed to modprobe via for_each_kmod_dep.
This is strange because my guess is that "_mpargs" means
"extra arguments for modprobe".

Second, the leading "--" will be lopped when a leading pathname
is stripped via
	_mod=${_mod##*/}
It seems to me that a leading "--" should inhibit modification.

Here's the corresponding patch to current HEAD (from dracut-013.)

dracut-functions

@@ -919,7 +919,6 @@ instmods() {
                 fi
                 ;;
             --*)
-                _mod=${_mod##*/}
                 _mpargs+=" $_mod";;
             i2o_scsi) shift; continue;; # Do not load this diagnostic-only module
             *)  _mod=${_mod##*/}
@@ -942,7 +941,7 @@ instmods() {
                 # ok, load the module, all its dependencies, and any firmware
                 # it may require
                 for_each_kmod_dep install_kmod_with_fw $_mod \
-                    --set-version $kernel ${_moddirname}
+                    --set-version $kernel ${_moddirname} $_mpargs
                 ((_ret+=$?))
                 ;;
         esac