message: refactor: Put`TryParsePermissionFlags` in anonymous namespace
  It's only used inside `net_permissions.cpp`.
diff: @@ -16,6 +16,8 @@ const std::vector<std::string> NET_PERMISSIONS_DOC{
  "mempool (allow requesting BIP35 mempool contents)",
  };
  +namespace {
  +
  // The parse the following format "perm1,perm2@xxxxxx"
  bool TryParsePermissionFlags(const std::string str, NetPermissionFlags& output, size_t& readen, bilingual_str& error)
  {
  @@ -60,6 +62,8 @@ bool TryParsePermissionFlags(const std::string str, NetPermissionFlags& output,
  return true;
  }
  +}
  +
  std::vector<std::string> NetPermissions::ToStrings(NetPermissionFlags flags)
  {
  std::vector<std::string> strings;
  