Add an enable/disable argument to setDontFragment() in preparation for dynamic
enable/disable of peer path MTU discovery. Add getDontFragment() to get the
status of the don't fragment bit from a socket.
Updates #311
Co-authored-by: James Tucker <james@tailscale.com>
Signed-off-by: Val <valerie@tailscale.com>
Use IPV6_MTU_DISCOVER for setting don't fragment on IPv6 sockets on Linux (was
using IP_MTU_DISCOVER, the IPv4 arg).
Updates #311
Signed-off-by: Val <valerie@tailscale.com>
Make the debugknob variable name for enabling peer path MTU discovery match the
env variable name.
Updates #311
Signed-off-by: Val <valerie@tailscale.com>