This parameter should be optional as only the first core in the mask
will be used to repin all ovs-vswitchd threads.
Leaving this parameter blank (and as a consequence, not setting
'dpdk-lcore-mask') allows all non-dpdk threads to float on the original
cpu set.
Change-Id: Ia9e001e2b1987f00a960cdf106eaa8e84dc4d71a
Signed-off-by: Christophe Fontaine <cfontain@redhat.com>