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>

rpcserver.go

@@ -3769,7 +3769,7 @@ func marshalDbEdge(edgeInfo *channeldb.ChannelEdgeInfo,
 			MinHtlc:          int64(c1.MinHTLC),
 			FeeBaseMsat:      int64(c1.FeeBaseMSat),
 			FeeRateMilliMsat: int64(c1.FeeProportionalMillionths),
-			Disabled:         c1.Flags&lnwire.ChanUpdateDisabled != 0,
+			Disabled:         c1.ChannelFlags&lnwire.ChanUpdateDisabled != 0,
 		}
 	}
 
@@ -3779,7 +3779,7 @@ func marshalDbEdge(edgeInfo *channeldb.ChannelEdgeInfo,
 			MinHtlc:          int64(c2.MinHTLC),
 			FeeBaseMsat:      int64(c2.FeeBaseMSat),
 			FeeRateMilliMsat: int64(c2.FeeProportionalMillionths),
-			Disabled:         c2.Flags&lnwire.ChanUpdateDisabled != 0,
+			Disabled:         c2.ChannelFlags&lnwire.ChanUpdateDisabled != 0,
 		}
 	}