lora/lorawan: refactor shared functionality for ChannelUS, etc into embedded type

named channel, do the same for RegionSettings, and then change RegionSettings to
just Settings to avoid the redundant naming.

Signed-off-by: deadprogram <ron@hybridgroup.com>

lora/lorawan/region/channel.go

@@ -0,0 +1,42 @@
+package region
+
+type Channel interface {
+	Next() bool
+	Frequency() uint32
+	Bandwidth() uint8
+	SpreadingFactor() uint8
+	CodingRate() uint8
+	PreambleLength() uint16
+	TxPowerDBm() int8
+	SetFrequency(v uint32)
+	SetBandwidth(v uint8)
+	SetSpreadingFactor(v uint8)
+	SetCodingRate(v uint8)
+	SetPreambleLength(v uint16)
+	SetTxPowerDBm(v int8)
+}
+
+type channel struct {
+	frequency       uint32
+	bandwidth       uint8
+	spreadingFactor uint8
+	codingRate      uint8
+	preambleLength  uint16
+	txPowerDBm      int8
+}
+
+// Getter functions
+func (c *channel) Frequency() uint32      { return c.frequency }
+func (c *channel) Bandwidth() uint8       { return c.bandwidth }
+func (c *channel) SpreadingFactor() uint8 { return c.spreadingFactor }
+func (c *channel) CodingRate() uint8      { return c.codingRate }
+func (c *channel) PreambleLength() uint16 { return c.preambleLength }
+func (c *channel) TxPowerDBm() int8       { return c.txPowerDBm }
+
+// Set functions
+func (c *channel) SetFrequency(v uint32)      { c.frequency = v }
+func (c *channel) SetBandwidth(v uint8)       { c.bandwidth = v }
+func (c *channel) SetSpreadingFactor(v uint8) { c.spreadingFactor = v }
+func (c *channel) SetCodingRate(v uint8)      { c.codingRate = v }
+func (c *channel) SetPreambleLength(v uint16) { c.preambleLength = v }
+func (c *channel) SetTxPowerDBm(v int8)       { c.txPowerDBm = v }