When this property is TRUE, IP configuration can continue as long
as at least on IP configuration type succeeds.  This allows
connections to networks where the user does not necessarily know
whether the network supports IPv4 or IPv6 and does not require
that both complete succesfully.

Since most of the time the user doesn't really care what type
of connectivity they have, as long as they have *some* connectivity,
this allows better "Just Works" behavior as long as the system
settings plugins and connection editors/applets use the right
defaults.

Suggested defaults for may-fail are:

IPv4: no (ie, require IPv4 connectivity)
IPv6: yes (ie, do not require IPv6 connectivity)

Users who require a specific type of connectivity are probably
knowlegable enough to check the box as needed for their network.