Upgrade to tcpdump 4.7.4.

Bug: http://b/24902618
Change-Id: I7c3605015d90453b0a8c339b1774e285796f8775
diff --git a/version.c b/version.c
index 6481d27..e7db708 100644
--- a/version.c
+++ b/version.c
@@ -1 +1 @@
-const char version[] = "4.5.1";
+const char version[] = "4.7.4";