vlan: Fix musl build error

caddr_t is legacy BSD and should be avoided [1]. While glibc may still
use __caddr_t as the type, Linux kernel does not (it is "void __user *
ifru_data").

This fixes compile errors with the musl libc:

../src/ap/vlan_init.c: In function 'br_delif':
../src/ap/vlan_init.c:218:18: error: '__caddr_t' undeclared (first use in this function)
  ifr.ifr_data = (__caddr_t) args;

[1] http://stackoverflow.com/questions/6381526/what-is-the-significance-of-caddr-t-and-when-is-it-used

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>

src/ap/vlan_init.c

@@ -280,7 +280,7 @@ static int br_delif(const char *br_name, const char *if_name)
 	args[1] = if_index;
 
 	os_strlcpy(ifr.ifr_name, br_name, sizeof(ifr.ifr_name));
-	ifr.ifr_data = (__caddr_t) args;
+	ifr.ifr_data = (void *) args;
 
 	if (ioctl(fd, SIOCDEVPRIVATE, &ifr) < 0 && errno != EINVAL) {
 		/* No error if interface already removed. */
@@ -331,7 +331,7 @@ static int br_addif(const char *br_name, const char *if_name)
 	args[1] = if_index;
 
 	os_strlcpy(ifr.ifr_name, br_name, sizeof(ifr.ifr_name));
-	ifr.ifr_data = (__caddr_t) args;
+	ifr.ifr_data = (void *) args;
 
 	if (ioctl(fd, SIOCDEVPRIVATE, &ifr) < 0) {
 		if (errno == EBUSY) {
@@ -459,7 +459,7 @@ static int br_getnumports(const char *br_name)
 
 	os_memset(ifindices, 0, sizeof(ifindices));
 	os_strlcpy(ifr.ifr_name, br_name, sizeof(ifr.ifr_name));
-	ifr.ifr_data = (__caddr_t) arg;
+	ifr.ifr_data = (void *) arg;
 
 	if (ioctl(fd, SIOCDEVPRIVATE, &ifr) < 0) {
 		wpa_printf(MSG_ERROR, "VLAN: %s: BRCTL_GET_PORT_LIST "