copy_filename: constify "src" arg

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/net/net.c b/net/net.c
index d5a5429..7576419 100644
--- a/net/net.c
+++ b/net/net.c
@@ -1865,7 +1865,7 @@
 	ip->ip_sum   = ~NetCksum((uchar *)ip, IP_HDR_SIZE_NO_UDP / 2);
 }
 
-void copy_filename (char *dst, char *src, int size)
+void copy_filename (char *dst, const char *src, int size)
 {
 	if (*src && (*src == '"')) {
 		++src;