SS_ASSERTINPROG
KKASSERT((so->so_state & SS_ASSERTINPROG) == 0);
so->so_state = head->so_state | SS_NOFDREF | SS_ASSERTINPROG;
soclrstate(so, SS_ASSERTINPROG);
soclrstate(so, SS_ASSERTINPROG);
KKASSERT((so->so_state & SS_ASSERTINPROG) == 0);
KKASSERT((so->so_state & SS_ASSERTINPROG) == 0);