netlib: Add support for adding/removing VLAN device

[HedongGao]

Summary

The Nuttx network protocol stack supports the Vlan module, and netlib needs to support Vlan related apis.

Impact

Users can add or delete Vlan interfaces through the netlib api interface.

Testing

`
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <netutils/netlib.h>

#define TEST_IFNAME "eth0" // Change to your actual base interface name
#define TEST_VLANID 100 // VLAN ID to test
#define TEST_VLANIF "eth0.100" // Expected VLAN interface name

int main(void)
{
int ret;

printf("Testing netlib_add_vlan()...\n");
ret = netlib_add_vlan(TEST_IFNAME, TEST_VLANID);
if (ret == 0)
{
    printf("netlib_add_vlan: SUCCESS (added VLAN %d to %s)\n", TEST_VLANID, TEST_IFNAME);
}
else
{
    printf("netlib_add_vlan: FAILED (errno=%d: %s)\n", errno, strerror(errno));
    return 1;
}

// Optionally, you can check if the VLAN interface exists here
// For simplicity, we just try to delete it

// printf("Testing netlib_del_vlan()...\n");
// ret = netlib_del_vlan(TEST_VLANIF);
// if (ret == 0)
// {
// printf("netlib_del_vlan: SUCCESS (deleted VLAN interface %s)\n", TEST_VLANIF);
// }
// else
// {
// printf("netlib_del_vlan: FAILED (errno=%d: %s)\n", errno, strerror(errno));
// return 1;
// }

printf("VLAN add/delete test completed.\n");
return 0;

}
`