samples: common: improvements in net_connect()

[mniestroj]

Those improvements affect mostly esp32 and mimxrt1060_evkb platforms, which require waiting for specific condition on network interface, before it can be used by net_connect() implementation.

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 66eb723):

https://golioth-zephyr-sdk-doxygen-dev--pr290-net-connect-wait-o2sjvg3k.web.app

_{(expires Sat, 01 Oct 2022 06:06:13 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}