ppp: update to 2.5.2

ppp: update to 2.5.2

This is a minor upgrade that mainly fixes some compilation errors
and remove old unused code.

The Makefile has been reorganized. Now all package make parameters
are passed as configure arguments instead of environment variables.
The compilation dependencies remain the same as ppp v2.5.1 and the
package size changes are negligible.

Change log:
https://github.com/ppp-project/ppp/blob/v2.5.2/README#L70

Upstreamed patches:
101-pppd-crypto-fix-build-without-openssl.patch [1]
102-pppd-make-pid-directory-before-create-the-pid-file.patch [2]
103-pppd-crypto-fix-gcc-14-build.patch [3]

[1] https://github.com/ppp-project/ppp/commit/5f6eabdb6666d914e0f8feb3facfa591dee75a1f
[2] https://github.com/ppp-project/ppp/commit/734bc0438e78b7c7cd34acfce3a4ec119d9a50b6
[3] https://github.com/ppp-project/ppp/commit/ac269dbf7c142371cd975c775c6171707ac4dde8

Signed-off-by: Shiji Yang <yangshiji66@qq.com>
Link: https://github.com/openwrt/openwrt/pull/17477
Signed-off-by: Nick Hainke <vincent@systemli.org>