dpdk-ovs: fix undefined refs to dlopen on Fedora

Update the Makefiles for openvswitch and qemu to link with libdl.so to
fix errors like on Fedora build hosts:
eal.c:(.text+0xf07): undefined reference to `dlopen'

Signed-off-by: Paul Barrette <paul.barrette@windriver.com>
Reviewed-by: Mark D. Gray <mark.d.gray@intel.com>