Fuchsia does not have UIDs, we use the MARK_2 domain mark to store the
UID of the process that created the sockets when the socket was created
by a process running in Starnix. This mark should be left unset otherwise.
MARK_1 domain is used to store the SO_MARK value set by Starnix
processes. If a mark in this domain is absent, it will be reported to
applications as a 0 since that is the default mark value on Linux.