Resolves ether_type incompatibility in packet.Frame

Frame:new() was populating the value as a 16-bit integer while
Frame:build_ether_frame() was expectng a two-byte string
Ethertype constants from various locations have been migrated to packet.lua

scripts/broadcast-ataoe-discover.nse

@@ -105,14 +105,14 @@ ATAoE = {
 -- Send a Config Info Request to the ethernet broadcast address
 -- @param iface table as returned by nmap.get_interface_info()
 local function sendConfigInfoRequest(iface)
-  local ETHER_BROADCAST, P_ATAOE = "ff:ff:ff:ff:ff:ff", 0x88a2
+  local ETHER_BROADCAST = "ff:ff:ff:ff:ff:ff"
   local req = ATAoE.ConfigInfoRequest:new()
   local tag = req.tag
 
   local p = packet.Frame:new()
   p.mac_src = iface.mac
   p.mac_dst = packet.mactobin(ETHER_BROADCAST)
-  p.ether_type = string.pack(">I2", P_ATAOE)
+  p.ether_type = packet.ETHER_TYPE_ATAOE
   p.buf = tostring(req)
   p:build_ether_frame()
 

scripts/broadcast-dhcp-discover.nse

@@ -147,8 +147,7 @@ local function dhcp_listener(sock, iface, macaddr, options, timeout, xid, result
   -- Add the Ethernet header
   frame:build_ether_frame(
     "\xff\xff\xff\xff\xff\xff",
-    iface.mac, -- can't use macaddr or we won't see response
-    packet.ETHER_TYPE_IPV4)
+    iface.mac) -- can't use macaddr or we won't see response
 
   local dnet = nmap.new_dnet()
   dnet:ethernet_open(iface.device)