SmartConfig and ETH need some work to adapt to the new API

* Add generic IP calculations

Add:
calculateNetworkID(IPAddress ip, IPAddress subnet) => Calculate the network id using the ip and subnet (e.g. 192.168.0.0)
calculateBroadcast(IPAddress ip, IPAddress subnet) => Calculate the broadcast ip using the ip and subnet (e.g. 192.168.0.255)
calculateSubnetCIDR(IPAddress subnetMask) => Calculate the subnet CIDR using the subnet (e.g. 24)

Add:
broadcastIP() => Retrieve the network id (e.g. 192.168.0.0)
networkID() => Retrieve the broadcast IP (e.g. 192.168.0.255)
subnetCIDR() => Retrieve the subnet CIDR (e.g. 24)

Add:
broadcastIP() => Retrieve the network id (e.g. 192.168.0.0)
networkID() => Retrieve the broadcast IP (e.g. 192.168.0.255)
subnetCIDR() => Retrieve the subnet CIDR (e.g. 24)

Add:
softAPBroadcastIP() => Retrieve the network id (e.g. 192.168.0.0)
softAPNetwrokID() => Retrieve the broadcast IP (e.g. 192.168.0.255)
softAPSubnetCIDR() => Retrieve the subnet CIDR (e.g. 24)

* Update mDNS and LEDC

* update toolchain

* Update IDF to 1c3dd23

* Advertise the board variant for Arduino OTA

* Add generic variant definition for mDNS

* Allow configuration of Ethernet PHY clock source
Refer to https://github.com/espressif/esp-idf/pull/1127
The internal APLL can be used to generate the 50MHz clock for the internal EMAC and the external Ethernet PHY.
The clock can either be input on GPIO0 (as before) or output on GPIO0, GPIO16 or GPIO17 (only GPIO17 extensively tested).
New example available.

* Allow configuration of Ethernet PHY clock source
Refer to https://github.com/espressif/esp-idf/pull/1127
The internal APLL can be used to generate the 50MHz clock for the internal EMAC and the external Ethernet PHY.
The clock can either be input on GPIO0 (as before) or output on GPIO0, GPIO16 or GPIO17 (only GPIO17 extensively tested).
New example available.

Fixes: https://github.com/espressif/arduino-esp32/issues/553