changed: Make (dvdplayer) network buffer more flexible/configurable

This is an improvement/change to the alwaysforcebuffer as.xml option that was implemented some time ago. I've changed the as.xml setting into an uint to allow us to set different buffer modes:
* 0) No buffer
* 1) Only buffer true internet filesystems (streams) (http, etc.)
* 2) Buffer all internet filesystems (like 2 but additionally also ftp, webdav, etc.) (default)
* 3) Buffer all filesystems (including local)

They idea about this as that on platforms like ARM like RPi, using buffering (in combination with certain filesystems) may cause too much drain (cpu usage) on the system. This setting allows the user to tweak this to their liking/setup.