external/dhcpc: fix dns setting issue
external/dhcpc: fix dns setting issue

As lwip is upgrade to 2.0, the way dns server is set is changed.
The commit apply the way lwip 2.0 provided to set dns server properly.

JeonginKim/TizenRT,btheosam/TizenRT,sunghan-chang/TizenRT,chanijjani/TizenRT,sunghan-chang/TizenRT,btheosam/TizenRT,jsdosa/TizenRT,pillip8282/TizenRT,sunghan-chang/TizenRT,jsdosa/TizenRT,JeonginKim/TizenRT,an4967/TizenRT,chanijjani/TizenRT,davidfather/TizenRT,Samsung/TizenRT,lokeshbv/TizenRT,junmin-kim/TizenRT,jeongchanKim/TizenRT,lokeshbv/TizenRT,chanijjani/TizenRT,jeongarmy/TizenRT,lokeshbv/TizenRT,jeongarmy/TizenRT,JeonginKim/TizenRT,sunghan-chang/TizenRT,JeonginKim/TizenRT,junmin-kim/TizenRT,junmin-kim/TizenRT,jeongarmy/TizenRT,jsdosa/TizenRT,junmin-kim/TizenRT,jeongarmy/TizenRT,btheosam/TizenRT,jeongarmy/TizenRT,davidfather/TizenRT,btheosam/TizenRT,jsdosa/TizenRT,jeongchanKim/TizenRT,davidfather/TizenRT,JeonginKim/TizenRT,lokeshbv/TizenRT,jeongchanKim/TizenRT,lokeshbv/TizenRT,an4967/TizenRT,jeongchanKim/TizenRT,junmin-kim/TizenRT,davidfather/TizenRT,pillip8282/TizenRT,Samsung/TizenRT,HONGCHAEHEE/TizenRT,lokeshbv/TizenRT,an4967/TizenRT,Samsung/TizenRT,sunghan-chang/TizenRT,davidfather/TizenRT,junmin-kim/TizenRT,sunghan-chang/TizenRT,Samsung/TizenRT,jeongchanKim/TizenRT,jsdosa/TizenRT,jsdosa/TizenRT,Samsung/TizenRT,HONGCHAEHEE/TizenRT,an4967/TizenRT,pillip8282/TizenRT,HONGCHAEHEE/TizenRT,jeongchanKim/TizenRT,HONGCHAEHEE/TizenRT,an4967/TizenRT,JeonginKim/TizenRT,jeongarmy/TizenRT,HONGCHAEHEE/TizenRT,pillip8282/TizenRT,junmin-kim/TizenRT,chanijjani/TizenRT,pillip8282/TizenRT,jeongchanKim/TizenRT,btheosam/TizenRT,sunghan-chang/TizenRT,jsdosa/TizenRT,pillip8282/TizenRT,chanijjani/TizenRT,an4967/TizenRT,HONGCHAEHEE/TizenRT,chanijjani/TizenRT,pillip8282/TizenRT,btheosam/TizenRT,an4967/TizenRT,Samsung/TizenRT,davidfather/TizenRT,Samsung/TizenRT,davidfather/TizenRT,chanijjani/TizenRT,jeongarmy/TizenRT