ls-remote: set packet_trace_identity(<name>)

ls-remote: set packet_trace_identity(<name>)

Set packet_trace_identity() for ls-remote. This replaces the generic
"git" identity in GIT_TRACE_PACKET=<file> traces to "ls-remote", e.g.:

    [...] packet:  upload-pack> version 2
    [...] packet:  upload-pack> agent=git/2.32.0-dev
    [...] packet:    ls-remote< version 2
    [...] packet:    ls-remote< agent=git/2.32.0-dev

Where in an "git ls-remote file://<path>" dialog ">" is the sender (or
"to the server") and "<" is the recipient (or "received by the
client").

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>