Change qlog file extension to .sqlog

Change qlog file extension to .sqlog because upstream ngtcp2 moves to
JSON-SEQ streaming qlog format.

src/h2load.cc

@@ -2245,11 +2245,10 @@ Options:
               to buffering.  Status code is -1 for failed streams.
   --qlog-file-base=<PATH>
               Enable qlog output and specify base file name for qlogs.
-              Qlog  is emitted  for each connection.
-              For  a  given  base  name "base", each  output file name
-              becomes  "base.M.N.qlog"  where M is worker ID  and N is
-              client ID (e.g. "base.0.3.qlog").
-              Only effective in QUIC runs.
+              Qlog is emitted  for each connection.  For  a given base
+              name   "base",    each   output   file    name   becomes
+              "base.M.N.sqlog" where M is worker ID and N is client ID
+              (e.g. "base.0.3.sqlog").  Only effective in QUIC runs.
   --connect-to=<HOST>[:<PORT>]
               Host and port to connect  instead of using the authority
               in <URI>.

src/h2load_quic.cc

@@ -441,7 +441,7 @@ int Client::quic_init(const sockaddr *local_addr, socklen_t local_addrlen,
     path += util::utos(worker->id);
     path += '.';
     path += util::utos(id);
-    path += ".qlog";
+    path += ".sqlog";
     quic.qlog_file = fopen(path.c_str(), "w");
     if (quic.qlog_file == nullptr) {
       std::cerr << "Failed to open a qlog file: " << path << std::endl;

src/shrpx.cc

@@ -3353,7 +3353,7 @@ HTTP/3 and QUIC:
               frontend QUIC  connections.  A qlog file  is created per
               each QUIC  connection.  The  file name is  ISO8601 basic
               format, followed by "-", server Source Connection ID and
-              ".qlog".
+              ".sqlog".
   --frontend-quic-require-token
               Require an address validation  token for a frontend QUIC
               connection.   Server sends  a token  in Retry  packet or

src/shrpx_http3_upstream.cc

@@ -2704,7 +2704,7 @@ int Http3Upstream::open_qlog_file(const StringRef &dir,
       util::format_iso8601_basic(buf.data(), std::chrono::system_clock::now());
   path += '-';
   path += util::format_hex(scid.data, scid.datalen);
-  path += ".qlog";
+  path += ".sqlog";
 
   int fd;