wireshark: Adapt to wireshark-4.6.0

wireshark: Adapt to wireshark-4.6.0

The main difference is that wmem_packet_scope() is gone [1] but
the packet_info struct has 'pool` member which points to the
allocator used for given packet.

Unfortunately, while we were given pointer to packet_info at the
entry level to our dissector (dissect_libvirt() ->
tcp_dissect_pdus() -> dissect_libvirt_message()) it was never
propagated to generated/primitive dissectors.

But not all dissectors need to allocate memory, so mark the new
argument as unused. And while our generator could be rewritten so
that the argument is annotated as unused iff it's really unused,
I couldn't bother rewriting it. It's generated code after all.
Too much work for little gain.

Another significant change is that val_to_str() now requires new
argument: pointer to allocator to use because it always allocates
new memory [2][3].

1: https://gitlab.com/wireshark/wireshark/-/commit/5ca5c9ca372e06881b23ba9f4fdcb6b479886444
2: https://gitlab.com/wireshark/wireshark/-/commit/b63599762468e4cf1783419a5556377604d344bb
3: https://gitlab.com/wireshark/wireshark/-/commit/84799be215313e61b83a3eaf074f89d6ee349b8c
Resolves: https://gitlab.com/libvirt/libvirt/-/issues/823
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>