adb: fix deadlock in kick_all_transports.

Previously, kick_all_transports would deadlock if there were any
inaccessible transports, because the transport kick function would call
unregister_usb_transport, which attempts to take the already-held
transport lock.

Fix this by switching the transport lock over to a recursive mutex.

Test: manual
Change-Id: If61296ff4745e1699f3e216811c1383582627604