Add SentExchange to Contact UDP broadcast

[ny4i]

N1MM added a new field to the contact UDP packet. It is called . For ARRl Field Day for example, it is 1A WCF. This is the exchange we send to the other station.

To maintain consistency with the standard, add this field to the contact broadcast.

Here is the latest example of the entire contact broadcast for reference and validation:

<contactinfo>
    <app>N1MM</app>
    <contestname>FD</contestname>
    <dbname>ham.s3db</dbname>
    <contestnr>2</contestnr>
    <timestamp>2024-06-05 13:21:18</timestamp>
    <mycall>NY4I</mycall>
    <band>3.5</band>
    <rxfreq>360000</rxfreq>
    <txfreq>360000</txfreq>
    <operator>W4UB</operator>
    <mode>LSB</mode>
    <call>W1AW</call>
    <countryprefix>K</countryprefix>
    <wpxprefix>W1</wpxprefix>
    <stationprefix>NY4I</stationprefix>
    <continent>NA</continent>
    <snt>59</snt>
    <sntnr>2</sntnr>
    <rcv>59</rcv>
    <rcvnr>0</rcvnr>
    <gridsquare></gridsquare>
    <exchange1>1F</exchange1>
    <section>CT</section>
    <comment></comment>
    <qth></qth>
    <name></name>
    <power></power>
    <misctext></misctext>
    <zone>5</zone>
    <prec></prec>
    <ck>0</ck>
    <ismultiplier1>0</ismultiplier1>
    <ismultiplier2>0</ismultiplier2>
    <ismultiplier3>0</ismultiplier3>
    <points>1</points>
    <radionr>1</radionr>
    <run1run2>1</run1run2>
    <RoverLocation></RoverLocation>
    <RadioInterfaced>0</RadioInterfaced>
    <NetworkedCompNr>0</NetworkedCompNr>
    <IsOriginal>True</IsOriginal>
    <NetBiosName>BEEPC-OFFICE</NetBiosName>
    <IsRunQSO>0</IsRunQSO>
    <StationName>BEEPC-OFFICE</StationName>
    <ID>9eeab0ae8fbf42cbabf50cbe3890a8a5</ID>
    <IsClaimedQso>1</IsClaimedQso>
    <oldtimestamp>2024-06-05 13:21:18</oldtimestamp>
    <oldcall>W1AW</oldcall>
    <SentExchange>1A WCF</SentExchange>
</contactinfo>