Tools: properly handle the keyboard interrupt (#2083)

Many tools rely on the user to type Ctrl-C to end, but don't actually
catch the keyboard interrupt and thus show an ugly backtrace when it
happens. Let's catch the interrupt.
diff --git a/tools/tcpstates.py b/tools/tcpstates.py
index 1444b31..4a21f02 100755
--- a/tools/tcpstates.py
+++ b/tools/tcpstates.py
@@ -386,4 +386,7 @@
 b["ipv4_events"].open_perf_buffer(print_ipv4_event, page_cnt=64)
 b["ipv6_events"].open_perf_buffer(print_ipv6_event, page_cnt=64)
 while 1:
-    b.perf_buffer_poll()
+    try:
+        b.perf_buffer_poll()
+    except KeyboardInterrupt:
+        exit()