Use strncpy when populating struct ifreq->ifr_name

We already check that ifname will fit into ifr_name in main(), but in
case do_ifreq gets called from elsewhere, use strncpy() instead of
strcpy().

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
diff --git a/inarp.c b/inarp.c
index 68e99ff..2ef7d41 100644
--- a/inarp.c
+++ b/inarp.c
@@ -114,7 +114,7 @@
 		const char *ifname, struct ifreq *ifreq)
 {
 	memset(ifreq, 0, sizeof(*ifreq));
-	strcpy(ifreq->ifr_name, ifname);
+	strncpy(ifreq->ifr_name, ifname, sizeof(ifreq->ifr_name));
 
 	return ioctl(fd, type, ifreq);
 }