Aded the "ngx_quic_hexdump" macro.

Aded the "ngx_quic_hexdump" macro.

ngx_quic_hexdump0(log, format, buffer, buffer_size);
    - logs hexdump of buffer to specified error log

    ngx_quic_hexdump0(c->log, "this is foo:", foo.data, foo.len);

ngx_quic_hexdump(log, format, buffer, buffer_size, ...)
    - same as hexdump0, but more format/args possible:

    ngx_quic_hexdump(c->log, "a=%d b=%d, foo is:", foo.data, foo.len, a, b);