Add iomux_from_timers() function to recover an IOMux from

the associated UCTimers

test/udp_heartbeat.c

@@ -1,5 +1,6 @@
 #define DEBUG
 #include <getopt.h>
+#include <assert.h>
 #include <errno.h>
 #include <stdlib.h>
 #include <time.h>
@@ -76,6 +77,7 @@ void peer_timer_cb(struct UCTimers *timers, struct UCTimer *timer)
     struct HBPeer *peer = UC_CONTAINER_OF(timer, struct HBPeer, timer);
     struct HBContext *ctx = timer->cookie_ptr;
     time_t now;
+    struct IOMux *mux;
 
     uc_timers_add(timers, timer, PEER_HB_MISS , 0);
     now = time(NULL);
@@ -85,6 +87,9 @@ void peer_timer_cb(struct UCTimers *timers, struct UCTimer *timer)
     }
 
     peer_send(ctx, peer);
+    //jsut a small test of iomux_from_timers
+    mux = iomux_from_timers(timers);
+    assert(mux == ctx->mux);
 }
 
 void peer_add_addr(struct HBContext *ctx, const struct sockaddr_in *addr)