adb: Fix two problems with device path implementation.

The commands that use "host-serial:<serial-number>:<request>"
service did not handle "-s usb:<path>".  The -s parameter is
passed as the serial number in the protocol and then matched
against either the serial number or device path.  However,
skip_host_serial() in sockets.c did not know about the usb:
syntax, the serial number was parsed incorrectly.  Before this
change:
	$ adb -s usb:1-4.1 get-state
	error: unknown host service
After:
	$ adb -s usb:1-4.1 get-state
	device

Code was added in find_transport() in transport.c to match device
paths, but find_transport() is only used for socket connections
so matching device paths is not needed.

Change-Id: I922cec963659dafadd0fbc8fa36dee3b55fe366c
Signed-off-by: Scott Anderson <saa@android.com>