main/ppp: upgrade to 2.5.1
remove 0001-Revert-lock-path-to-var-lock-435.patch, fixed upstream refactor 0011-build-sys-don-t-put-connect-errors-log-to-etc-ppp.patch to apply to this pppd version
remove 0001-Revert-lock-path-to-var-lock-435.patch, fixed upstream refactor 0011-build-sys-don-t-put-connect-errors-log-to-etc-ppp.patch to apply to this pppd version