Returns the number of bytes required for an IPv6 routing header.
    Format
      #include  <in6.h>
      size_t inet6_rth_space  ( int type, int segments );

1  –  Arguments

 type
    Specifies the type of routing header. The valid value is IPV6_
    RTHDR_TYPE_0 for IPv6 routing header type 0.
 segments
    Specifies the number of segments or addresses that are to be
    included in the routing header. The valid value is from 0 to 127,
    inclusive.

2  –  Description

    This function determines the amount of space, in bytes, required
    for a routing header. Although the function returns the amount of
    space required, it does not allocate buffer space. This enables
    the application to allocate a larger buffer.
    If the application uses ancillary data, it must pass the returned
    length to CMSG_LEN() to determine the amount of memory required
    for the ancillary data object, including the cmsghdr structure.
                                   NOTE
       If an application wants to send other ancillary data
       objects, it must specify them to sendmsg() as a single msg_
       control buffer.

3  –  Return Values

    x                  Upon successful completion, the inet6_rth_
                       space() function returns the length, in bytes,
                       of the routing header and the specified number
                       of segments.
    0 (zero)           Failure, if the type is not supported or the
                       number of segments is invalid for the type of
                       routing header.