init: use FQName parse

FQName::FQName(string) could leave the FQName in an
invalid state, and so this constructor is being removed
and the mValid member is being removed.

Bug: 73774955
Test: boots + interface_start control messages received by init
Change-Id: I58d4a089c0a0f1c2cc5129c5e87321e7f6663b72