[wlan] Make WlanSoftmacBandCapability evolvable

Modifies the WlanSoftmacBandCapability struct to be a table.

Bug: 87050
Test: Test updated to use flexible types. Intel driver
      connects and pings on a wpa2 network.

Change-Id: If9dbd94270eb0dc796f8c8c593b0b2b214f5a844
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/674445
Reviewed-by: Dylan Swiggett <swiggett@google.com>
Reviewed-by: Rebecca Silberstein <silberst@google.com>
API-Review: Rebecca Silberstein <silberst@google.com>
Reviewed-by: Zhiyi Chen <zhiyichen@google.com>
Fuchsia-Auto-Submit: Sakthi Vignesh Radhakrishnan <rsakthi@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>