net/mpd5: fix some LCP negotiation problems

• Import upstream r2453: prevent endless LCP restarts in case of broken

peer or heavy packet drops. Allow 3 restarts then terminate LCP.
Let link redial restart it from the beginning, if configured.

• Import upstream r2454: fixes long-standing bug

known as "LCP: not converging" problem leaving link closed
with erroneously disabled redial.