The method used to set the high 6 bits (the
differentiated services codepoint) of the IPv4 TOS or
IPv6 Traffic Class in the outer IP header. A value of
-1 indicates that the bits are copied from the
payload's header. A value of -2 indicates that a
traffic conditioner is invoked and more information
may be available in a traffic conditioner MIB module.
A value between 0 and 63 inclusive indicates that the
bit field is set to the indicated value.
Note: instead of the name tunnelIfTOS, a better name
would have been tunnelIfDSCPMethod, but the existing
name appeared in RFC 2667 and existing objects cannot
be renamed.