ppp-udeb: Rewrite PPPoE access concentrator detection

Pascal Hambourgrequested to merge
pham/ppp:udeb-timeout into master

Timeout management during PPPoE access concentrator detection in ppp-udeb.postinst is broken:

  • busybox-udeb ps does not support -A;
  • all leading spaces in ps output are not trimmed properly so the PID may not be extracted correctly.
  • stalled pppoe-discovery processes are killed after the loop, so buffered output is not written to /tmp/probe-finished yet before it is read;

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1070753

Remove all this and manage timeout using pppoe-discovery options -Q, -a and -t. Set 3 attempts with 1-second timeout because it is unlikely that an access concentrator replies with more than 1-second delay, so the total timeout is 2x3x1=6 seconds.

Fixes: #1070753 Tested by the bug submitter

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