ppp: Update to version 2.5.1

ppp: Update to version 2.5.1

- Update from version commit e1266c7 to 2.5.1
- Version 2.5.1 has around 34 additional commits from e1266c7. To me all look minor
   changes, some related to other system types such as Solaris that we don't use.
- Update of rootfile
- They have added example to the configuration files to prevent accidental overwriting
   of configuration systems.
- Changelog - There is no longer any changelog provided. Even the one that used to
   exist for version 2.5.0 has been removed. The only option now is to look through the
   commits - https://github.com/ppp-project/ppp/commits/master/?before=d5aeec65752d4a9b3bb46771d0b221c4a4a6539e+35
- Some of the patches had to be updated as the changes were enough that some hunks did
   not get found for patching. Patch file number 6 has been removed as the sed lines are
   no longer to be found in the configure file. The other files that patched successfully
   were renamed to 2.5.1

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>