DHCP fixes

I am finding a few bugs in +TCP, or misunderstandings perhaps.
  1. For reliable receipt of the DHCP’d IP address for certain routers, dhcpMAXOPTIONLENGTHOFINTEREST must be set to 0, otherwise the loop ends before using the IP
  2. Option 61 (dhcpCLIENTIDENTIFIEROPTION_CODE) isn’t being set correctly. Byte 1 should be set to ethernet. To implement this: ~~~

define dhcpCLIENTIDENTIFIEROFFSET ( 6 )

define dhcpREQUESTEDIPADDRESS_OFFSET ( 14 )

define dhcpDHCPSERVERIPADDRESSOFFSET ( 20 )

//in prvSendDHCPRequest and prvSendDHCPDiscover dhcpCLIENTIDENTIFIEROPTION_CODE, 7, 1, 0, 0, 0, 0, 0, 0, ~~~