Make roughly work on signed integers.

This is needed for the stability aware code.

util.c

@@ -36,10 +36,15 @@ THE SOFTWARE.
 #include "babeld.h"
 #include "util.h"
 
-unsigned
-roughly(unsigned value)
+int
+roughly(int value)
 {
-    return value * 3 / 4 + random() % (value / 2);
+    if(value < 0)
+        return -roughly(-value);
+    else if(value <= 1)
+        return value;
+    else
+        return value * 3 / 4 + random() % (value / 2);
 }
 
 void

util.h

@@ -66,7 +66,7 @@ seqno_plus(unsigned short s, int plus)
     return ((s + plus) & 0xFFFF);
 }
 
-unsigned roughly(unsigned value);
+int roughly(int value);
 void timeval_minus(struct timeval *d,
                    const struct timeval *s1, const struct timeval *s2);
 unsigned timeval_minus_msec(const struct timeval *s1, const struct timeval *s2)