Fix missing-prototype errors in sample programs

Signed-off-by: Michael Schuster <michael@schuster.ms>
diff --git a/programs/test/udp_proxy.c b/programs/test/udp_proxy.c
index beaa8bd..bf06871 100644
--- a/programs/test/udp_proxy.c
+++ b/programs/test/udp_proxy.c
@@ -483,7 +483,7 @@
 } packet;
 
 /* Print packet. Outgoing packets come with a reason (forward, dupl, etc.) */
-void print_packet(const packet *p, const char *why)
+static void print_packet(const packet *p, const char *why)
 {
 #if defined(MBEDTLS_TIMING_C)
     if (why == NULL) {
@@ -527,7 +527,7 @@
 static inject_clihlo_state_t inject_clihlo_state;
 static packet initial_clihlo;
 
-int send_packet(const packet *p, const char *why)
+static int send_packet(const packet *p, const char *why)
 {
     int ret;
     mbedtls_net_context *dst = p->dst;
@@ -616,13 +616,13 @@
 static size_t prev_len;
 static packet prev[MAX_DELAYED_MSG];
 
-void clear_pending(void)
+static void clear_pending(void)
 {
     memset(&prev, 0, sizeof(prev));
     prev_len = 0;
 }
 
-void delay_packet(packet *delay)
+static void delay_packet(packet *delay)
 {
     if (prev_len == MAX_DELAYED_MSG) {
         return;
@@ -631,7 +631,7 @@
     memcpy(&prev[prev_len++], delay, sizeof(packet));
 }
 
-int send_delayed(void)
+static int send_delayed(void)
 {
     uint8_t offset;
     int ret;
@@ -663,7 +663,7 @@
 static unsigned char held[2048] = { 0 };
 #define HOLD_MAX 2
 
-int handle_message(const char *way,
+static int handle_message(const char *way,
                    mbedtls_net_context *dst,
                    mbedtls_net_context *src)
 {