main/ppp: upgrade to 2.4.8

change source to github ppp repository remove defaultroute-metric.3.patch, fixed upstream remove prepare() function and use default change builddir and remove _builddir fix musl-fix-headers.patch add fix-pppd-magic.h.patch (split out of the musl-fix-headers.patch and addapted) add fix-pppd-pppoe.h.patch (split out of the musl-fix-headers.patch and addapted) enable USE_CRYPT=y in pppd/Makefile.linux to use libcrypto, else it try to use des.h (which does not exist on Alpine).