[PATCH 0 of 4] QUIC path MTU discovery

[Roman Arutyunyan]

Updated PMTUD:

- Eliminated getting local interface MTU.  This was too intrusive and platform-
  dependent.

- Added timeout (1 sec) before each PMTUD iteration to reduce PMTUD traffic
  in short connections.

- Size search reimplemented.  MTU is increased by 256 bytes until failure,
  after which binary search is used.  Real life MTU will be around 1500, while
  initial payload size is 1200.  Doing binary search from 65k down to 1500 will
  produce a lot of failed syscalls and useless traffic.  Ascending from 1200
  to a first failre will be quick.

--
Roman Arutyunyan