replace single-char printf's with bb_putchar

diff --git a/networking/libiproute/ipaddress.c b/networking/libiproute/ipaddress.c
index 4bc87e7..3bf854e 100644
--- a/networking/libiproute/ipaddress.c
+++ b/networking/libiproute/ipaddress.c
@@ -41,7 +41,7 @@
 
 static void print_link_flags(unsigned flags, unsigned mdown)
 {
-	printf("<");
+	bb_putchar('<');
 	flags &= ~IFF_RUNNING;
 #define _PF(f) if (flags & IFF_##f) { \
 		  flags &= ~IFF_##f; \