LibAliasSetAliasPortRange
void LibAliasSetAliasPortRange(struct libalias *la, u_short port_low, u_short port_hi);
LibAliasSetAliasPortRange(ptr->lib, ptr->alias_port_lo, ptr->alias_port_hi);
LibAliasSetAliasPortRange(la, 0, 0); /* reinit like ipfw */
LibAliasSetAliasPortRange(la, 2000, 3000);
LibAliasSetAliasPortRange(la, 4000, 4001);
LibAliasSetAliasPortRange(la, 0, 0);