Title: pack_oneCsum()

pack_oneCsum() computes the checksum of a udp packet. It accomplishes this by computing the checksum (by calling oneC_sum() of each of the packet's buffers).

Note that a checksum is used to determine if errors occurred during the transmission of data.

pack_oneCsum() is very similar to icmp_pack_oneCsum(). The two functions probably should have been consolidated into one.