Display filter field names in the csv file

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From the tshark man page (also in the help output by -h):

-E <field print="" option=""> Set an option controlling the printing of fields when -T fields is selected.

Options are:

bom=y|n If y, prepend output with the UTF-8 byte order mark (hexadecimal ef, bb, bf). Defaults to n.

header=y|n If y, print a list of the field names given using -e as the first line of the output; the field name will be separated using the same character as the field values. Defaults to n.

separator=/t|/s|<character> Set the separator character to use for fields. If /t tab will be used (this is the default), if /s, a single space will be used. Otherwise any character that can be accepted by the command line as part of the option may be used.

occurrence=f|l|a Select which occurrence to use for fields that have multiple occurrences. If f the first occurrence will be used, if l the last occurrence will be used and if a all occurrences will be used (this is the default).

aggregator=,|/s|<character> Set the aggregator character to use for fields that have multiple occurrences. If , a comma will be used (this is the default), if /s, a single space will be used. Otherwise any character that can be accepted by the command line as part of the option may be used.

quote=d|s|n Set the quote character to use to surround fields. d uses double-quotes, s single-quotes, n no quotes (the default).

So add -E header=y to your command line.