Fix close() issue

Fix close() mathod parameter type from jobject to jclass,
otherwise a call to close() method results in a following exception:

Exception in thread "main" java.lang.UnsatisfiedLinkError:
de.entropia.can.CanSocket._close(I)V
at de.entropia.can.CanSocket._close(Native Method)
at de.entropia.can.CanSocket.close(CanSocket.java:405)

Reported and fixed by Sandro Anders.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>