lib/dgram.js fix 80 line issue
Revert "udp: pass the length of the sent size to the callback"

This reverts commit 4d0d0fa8fd8a32b2cac68899d1af25a0cc6d3cc0.
lib/dgram.js use trevnorris method to pass length
test-dgram-empty-packet.js
test-dgram-send-callback-buffer-length
test-dgram-send-empty-buffer
test-dgram-send-empty-buffer