multi: partition lnwire.ChanUpdateFlag into ChannelFlags and MessageFlags

In this commit:

* we partition lnwire.ChanUpdateFlag into two (ChanUpdateChanFlags and
ChanUpdateMsgFlags), from a uint16 to a pair of uint8's

* we rename the ChannelUpdate.Flags to ChannelFlags and add an
additional MessageFlags field, which will be used to indicate the
presence of the optional field HtlcMaximumMsat within the ChannelUpdate.

* we partition ChannelEdgePolicy.Flags into message and channel flags.
This change corresponds to the partitioning of the ChannelUpdate's Flags
field into MessageFlags and ChannelFlags.

Co-authored-by: Johan T. Halseth <johanth@gmail.com>

autopilot/graph.go

@@ -229,7 +229,8 @@ func (d *databaseChannelGraph) addRandChannel(node1, node2 *btcec.PublicKey,
 		MinHTLC:                   1,
 		FeeBaseMSat:               10,
 		FeeProportionalMillionths: 10000,
-		Flags:                     0,
+		MessageFlags:              0,
+		ChannelFlags:              0,
 	}
 
 	if err := d.db.UpdateEdgePolicy(edgePolicy); err != nil {
@@ -243,7 +244,8 @@ func (d *databaseChannelGraph) addRandChannel(node1, node2 *btcec.PublicKey,
 		MinHTLC:                   1,
 		FeeBaseMSat:               10,
 		FeeProportionalMillionths: 10000,
-		Flags:                     1,
+		MessageFlags:              0,
+		ChannelFlags:              1,
 	}
 	if err := d.db.UpdateEdgePolicy(edgePolicy); err != nil {
 		return nil, nil, err