Automatically probe the path MTU to a peer when peer MTU is enabled, but do not
use the MTU information for anything yet.
Updates #311
Signed-off-by: Val <valerie@tailscale.com>
Replace CanPMTUD() with ShouldPMTUD() to check if peer path MTU discovery should
be enabled, in preparation for adding support for enabling/disabling peer MTU
dynamically.
Updated #311
Signed-off-by: Val <valerie@tailscale.com>
Claire Wang
Val
Brad Fitzpatrick