[CTS] Clarify CTS assert message for missing RTT AP support

Add a much more verbose message for the common failure case in which
the CTS is run without an AP which supports IEEE 802.11mc / RTT. That
may help speed up issue resolution.

Bug: 116849381
Test: atest WifiRttTest
Change-Id: I4ea3fbe17563f0087a013cbf48f7f601fec7e363
1 file changed
tree: 4f91702b141cf06e4bbaf02dd274fdd1230e8a6a
  1. tests/