linuxPackages.virtualboxGuestAdditions: apply mp-r0drv-linux.c patch

These don't use a the virtualbox sources, but an iso as src, and we need
to add the kernel 5.3 patch aswell.

As for some reason the source files are present on the .iso with Windows
Line endings (sic!), call dos2unix first.

Unfortunately, we can't use the same kernel-5.3-fix.patch as virtualbox
itself, as some files are missing and paths are different.