staging: usbip: userspace: add gitignore file

There are a bunch of automatically generated files that git
should not care about.
Signed-off-by: NIlija Hadzic <ihadzic@research.bell-labs.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/usbip/userspace/.gitignore

+Makefile
+Makefile.in
+aclocal.m4
+autom4te.cache/
+config.guess
+config.h
+config.h.in
+config.log
+config.status
+config.sub
+configure
+depcomp
+install-sh
+libsrc/Makefile
+libsrc/Makefile.in
+libtool
+ltmain.sh
+missing
+src/Makefile
+src/Makefile.in
+stamp-h1
+libsrc/libusbip.la
+libsrc/libusbip_la-names.lo
+libsrc/libusbip_la-usbip_common.lo
+libsrc/libusbip_la-usbip_host_driver.lo
+libsrc/libusbip_la-vhci_driver.lo
+src/usbip
+src/usbipd