samples: sockets: echo_async: Make IPV6 optional
samples: sockets: echo_async: Make IPV6 optional

Changing the example to not use IPv6 when it is not configured,
given IPv6 is not enabled on some platforms such as cc3220sf_launchxl.

Signed-off-by: Vincent Wan <0da4a49376daf88459b96a63301ecd5aff2f3b80@linaro.org>

zephyrproject-rtos/zephyr,galak/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,Vudentz/zephyr,ldts/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,ldts/zephyr,ldts/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr