In the past, RCU grace-period initialization excluded CPU-hotplug
operations, but this is no longer the case.  This commit therefore
removed an outdated comment in rcu_gp_init() claiming that these
are excluded.
Reported-by: NLihao Liang <lihao.liang@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>