openvswitch: Use libtool and allow building shared libs

openvswitch: Use libtool and allow building shared libs

Currently openvswitch builds all libraries static only. However,
libopenvswitch is linked into nearly all openvswitch executables
making it hardly possible to run openvswitch on embedded devices
(for example running OpenWrt).

Convert openvswitch to use libtool for building its internal libs.
This allows "--enable-shared" and "--enable-static" as configure
arguments. Default is "--disable-shared" thus keeping the current
behavior with the only change that static libs are installed by
"make install".

Since the openvswitch library interfaces are internal and thus not
stable (yet) encode the openvswitch version into the library name:
libopenvswitch-2.0.90.so

Binary size is reduced to around 1/3 when using shared libs.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>