Use TLS_client_method and TLS_server_method

Use ngtcp2_conn_state as type for state field

When compiling with the flag -Wswitch-enum there are a number of
warnings like the following:
ngtcp2_conn.c:7960:11: warning:
7 enumeration values not handled in switch:
  'NGTCP2_CS_CLIENT_INITIAL',
  'NGTCP2_CS_CLIENT_WAIT_HANDSHAKE',
  'NGTCP2_CS_CLIENT_TLS_HANDSHAKE_FAILED'... [-Wswitch]
  switch (conn->state) {

This commit adds a default clause to avoid this as they are reported as
errors on the CI server and failing the build.

This commit changes the TLS_method() used by the client and server to
use more specific TLS_client_method() and TLS_server_method().

The main difference between these two are ossl_statem_accept is
undefined for the client, and ossl_statem_connect is undefined for the
server:

IMPLEMENT_tls_meth_func(TLS_ANY_VERSION, 0, 0,
                        TLS_server_method,
                        ossl_statem_accept,
                        ssl_undefined_function, TLSv1_2_enc_data)

IMPLEMENT_tls_meth_func(TLS_ANY_VERSION, 0, 0,
                        TLS_client_method,
                        ssl_undefined_function,
                        ossl_statem_connect, TLSv1_2_enc_data)

ossl_statem_accept and ossl_statem_connect are defined like this:

int ossl_statem_accept(SSL *s) {
    return state_machine(s, 1);
}
int ossl_statem_connect(SSL *s) {
    return state_machine(s, 0);
}

So they are both calling state_machine but with setting the server
parameter to 1 and 0 (for...

Move template.h into server.cc

Add Wireshark configuration steps

This commit suggests updating ngtcp2_conn's state field to be of type
ngtcp2_conn_state instead of type int.

This commit adds information about configuring Wireshark for analyzing
QUIC traffic.

Add inc_len_varint function to ngtcp2_crypto.c

Move template.h include to client.cc

Move ngtcp2_range.h into ngtcp2_gaptr.c

Remove unused assert.h includes

Check mmap's return value

Remove unused ngtcp2_macro.h includes

Remove redundant Buffer::bufsize()

Previously, when mmap() failed the client example crashed deep inside ngtcp2 on trying to access address 0xffffffffffffffff. This can happen for example if `--data` specifies a directory.

This commit moves the include of template.h into client.cc as it does
not seem to be used any longer by client.h.

Commit a7d6c8c4 ("Add
ngtcp2_acked_stream_data_offset callback") removed the field streambuf_
which was using the user-defined literal `_k` from template.h:

std::array<uint8_t, 32_k> streambuf_;

The header ngtcp2_gaptr.h does not use anything from ngtcp2_range.h and
this commit suggests moving the include to ngtcp2_gaptr.c instead.

This commit contains a suggestion to add a static function to reduce
some code duplication in ngtcp2_encode_transport_params.

It's now identical to size().

Remove redundant Buffer::head

`head` always equals `begin`. A subsequent diff can further simplify Buffer by removing bufsize(), which is now identical to size().

Remove unused ngtcp2_macro include in ngtcp2_qlog

Update ngtcp2_recv_crypto_data documentation

Use closure for scid and dcid generation

Remove unused parts of Buffer in example

Use char instead of string for \n in client.cc

This commit removes the include of ngtcp2_macro.h as it does not seem to
be used.