Work around compiler error for breaking strict-aliasing rules

This commit fixes the following warning on an ARM eabi/uClibc system.
helpers.c:86: error: dereferencing pointer 'a' does break strict-aliasing rules

The fix is trivial. Simply set IPv4 addressing scheme in the
struct ifreq instead of the struct sockaddr_in, whic is just
a pointer into the same ifreq anyway.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

helpers.c

@@ -83,7 +83,7 @@ void ifconfig(char *name, char *inet, char *mask, int up)
 
 	memset(&ifr, 0, sizeof (ifr));
 	strlcpy(ifr.ifr_name, name, IFNAMSIZ);
-	a->sin_family = AF_INET;
+	ifr.ifr_addr.sa_family = AF_INET;
 
 	if (up) {
 		inet_aton(inet, &a->sin_addr);