From: Fan Du

This patchset performs some small fix and enhancement
for current TCP PMTU as per RFC4821 with below changes:

Patch1/4: Set probe mss base to 1024 Bytes per RFC4821
Patch2/4: Do not double probe_size for each probing,
          use a simple binary search to gain maximum performance.
Patch3/4: When it comes to blackhole detection, shrink current
	  mss for next probing.
Patch4/4: Create a probe timer to detect enlarged path MTU.

Isn't the most likely problem PPPoE blackholes?
Where a reduction of the PMTU from 1500 to (IIRC) 1492 is
all that is required?

Would seem appropriate to test that value reasonable quickly.

	David