Add a "fork" of musl as //fusl.

fusl/src/network/if_nametoindex.c

Index: fusl/src/network/if_nametoindex.c
diff --git a/fusl/src/network/if_nametoindex.c b/fusl/src/network/if_nametoindex.c
new file mode 100644
index 0000000000000000000000000000000000000000..cb6ec054efbd971fc362bc7dd24c738fc12eb997
--- /dev/null
+++ b/fusl/src/network/if_nametoindex.c
@@ -0,0 +1,18 @@
+#define _GNU_SOURCE
+#include <net/if.h>
+#include <sys/socket.h>
+#include <sys/ioctl.h>
+#include <string.h>
+#include "syscall.h"
+
+unsigned if_nametoindex(const char *name)
+{
+	struct ifreq ifr;
+	int fd, r;
+
+	if ((fd = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0)) < 0) return -1;
+	strncpy(ifr.ifr_name, name, sizeof ifr.ifr_name);
+	r = ioctl(fd, SIOCGIFINDEX, &ifr);
+	__syscall(SYS_close, fd);
+	return r < 0 ? 0 : ifr.ifr_ifindex;
+}