Display warning if users does not provide CA cert in EAP config

Display an explicit warning in the WiFi configuration menu if
the user selects the option to not validate the EAP server (i.e.
does not provide a CA certificate) in an EAP configuration.

BUG: 26686071
Change-Id: I73620b60defdcf40865f8c67d5de24b5dad636f8
TEST: Warning appears when the abovementioned option is selected.