net/net: Clean up global variable shadowing

net/net: Clean up global variable shadowing

Fix:

  net/net.c:1680:35: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
  bool netdev_is_modern(const char *optarg)
                                    ^
  net/net.c:1714:38: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
  void netdev_parse_modern(const char *optarg)
                                       ^
  net/net.c:1728:60: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
  void net_client_parse(QemuOptsList *opts_list, const char *optarg)
                                                             ^
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/getopt.h:77:14: note: previous declaration is here
  extern char *optarg;                    /* getopt(3) external variables */
               ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231004120019.93101-4-philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>