modprobe: rework module insertion without tree traversing

modprobe: rework module insertion without tree traversing

The dependencies line that comes from modules.dep already contains all
the dependencies necessary to insert that module. Therefore modprobe
doesn't have to do the recursion between the modules in order to load a
module. All we have to do is to load in order:

For the module being loaded:
----------------------------

1. softdeps
2. deps
3. module
4. postdeps

For any of the dependencies:
----------------------------

1. softdeps
2. module
3. softdeps