In this commit, we now properly examine the Flag field within the
ChannelUpdate message as a bitfield. Before this commit we would
manually check the flags for zero or one. This was incorrect as a their
bit has now been defined. To properly dispatch the messages, we’ll now
treat it properly as a bitmask.
Add tests for new deDupedAnnouncements struct in gossiper_test.
Test the various functionalities of the struct - that empty
struct contains no announcements, that announcements of each type
can be added and properly de-duplicated, that the batch of
announcements is delivered correctly, and that after reset the
struct again contains no announcements.
