update pppd patch and build shell script, fix buildroot glibc build bug

guowenxue

2019-08-11 44b6985a5c9724e5f8b8f30000c5f022dee42863

linux-bsp/tarballs/linux-at91.tar.xz does not exist in tree dae258dae189cee8ca4e0cc69657077bc1f98d9e