Merge https://github.com/gpotter2/zeek.

Changes during merge:
  - Add dedicated test (w/ trace "client_timestamp_enabled.pcapng" from Cloudshark)
  - Change types from signed to unsigned.
  - Add cast for bit-shifting operand.
  - clang-format run

testing/btest/scripts/base/protocols/tcp/timestamp.zeek

@@ -0,0 +1,6 @@
+# @TEST-EXEC: zeek -b -C -r $TRACES/tcp/timestamp.pcap %INPUT
+# @TEST-EXEC: btest-diff .stdout
+
+event connection_SYN_packet(c: connection, pkt: SYN_packet) {
+        print pkt;
+}