bridge/vlan.c: bridge/vlan.c: fix build with gcc 14 on musl systems

bridge/vlan.c: bridge/vlan.c: fix build with gcc 14 on musl systems

On glibc based systems the definition of 'struct timeval' is pulled in
with inclusion of <stdlib.h> header, but on musl based systems it
doesn't work this way.  Missing definition triggers an
incompatible-pointer-types error with gcc 14 (warning on previous
versions of gcc):

../include/json_print.h:80:30: warning: 'struct timeval' declared inside parameter list will not be visible outside of this definition or declaration
   80 | _PRINT_FUNC(tv, const struct timeval *)
      |                              ^~~~~~~
../include/json_print.h:50:37: note: in definition of macro '_PRINT_FUNC'
   50 |                                     type value);                        \
      |                                     ^~~~
../include/json_print.h:80:30: warning: 'struct timeval' declared inside parameter list will not be visible outside of this definition or declaration
   80 | _PRINT_FUNC(tv, const struct timeval *)
      |                              ^~~~~~~
../include/json_print.h:55:45: note: in definition of macro '_PRINT_FUNC'
   55 |                                             type value)                 \
      |                                             ^~~~
../include/json_print.h: In function 'print_tv':
../include/json_print.h:58:48: error: passing argument 5 of 'print_color_tv' from incompatible pointer type [-Wincompatible-pointer-types]
   58 |                                                value);                  \
      |                                                ^~~~~
      |                                                |
      |                                                const struct timeval *

Signed-off-by: Gabi Falk <gabifalk@gmx.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>