iproute2: improved error messages

This patch improves many error messages as follows:
- For incorrect parameters, show the value of the offending parameter, rather than just say that it is incorrect
- Rephrased messages for clarity
- Rephrased to more `mainstream' english

Signed-off-by: Kees van Reeuwijk <reeuwijk@few.vu.nl>
diff --git a/ip/iproute.c b/ip/iproute.c
index c60156f..309cc87 100644
--- a/ip/iproute.c
+++ b/ip/iproute.c
@@ -1099,7 +1099,7 @@
 	int ret;
 
 	if (isatty(STDOUT_FILENO)) {
-		fprintf(stderr, "Not sending binary stream to stdout\n");
+		fprintf(stderr, "Not sending a binary stream to stdout\n");
 		return -1;
 	}
 
@@ -1445,7 +1445,7 @@
 	}
 
 	if (req.r.rtm_dst_len == 0) {
-		fprintf(stderr, "need at least destination address\n");
+		fprintf(stderr, "need at least a destination address\n");
 		exit(1);
 	}