Fix PAN crash due to fd mismatch

Fix PAN crash due to fd mismatch

A case, where tap read thread is always exist, Sometimes
data packets get recieved on older fd, which is not available.
which is causing assert due to fd mismatch in race condition.
when next pan connection is immediately available. If last pan
connection gets disconnected, then tap_read_thread should be
destroyed in btif context to fix this issue.

Bug: 24093456
Change-Id: Ic1053200a7be4c2091d6c394634831ca3fbd61df