Updating header comments with expected behavior

gtests/net/packetdrill/tests/bsd/tcp/listen/listen-incoming-no-tcp-flags.pkt

-// Test behavior when a listener gets an incoming packet that has
-// no TCP flags set.
+// Test behavior when a listener gets an incoming packet from
+// new sender on a non-established connection that
+// doesn't have any of the TCP flags set.
+// Listener should not send any response.
+// Checking if we can establish a connection with the
+// system after a connection reset.
 
 0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
 0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0