Check BR device count before initiating role switch

A case where DUT is acting as PANU device on BR/EDR link & also
acting as central on LE link. As LE link & PANU link need not to
be master & it's not a scatter-net scenario, because there is only
a BR link. So checking for BR device count before initiating role
switch to avoid continuous loop of role switches.

Cherry-picked from: https://partner-android-review.googlesource.com/#/c/376058/

Change-Id: I70e4041a71ba965f1f9e25729c3cfd20ae03d6b4
Bug: 23290136