Update PPP to 2.5.1

[Neustradamus]

Dear @pisilinux team, @ayhanyalcinsoy, @aydemir, @suvari, @ertugerata, @bferturk, @Rmys,

Can you update PPP to 2.5.1?

• https://github.com/pisilinux/main/tree/master/network/connection/ppp

Thanks in advance.