Photon/P1: WiFi.dnsServerIP()/WiFi.dhcpServerIP() support

[avtolstoy]

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Problem

See #1132

Solution

Implement the support in Photon/P1 wlan_hal.

Steps to Test

• wiring/no_fixture: WIFI_03_config

Example App

N/A

References

• Closes #1132
• [CH7828]
• spark/photon-wiced#19

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)