datapath: Don't call genlmsg_reply() under rcu_read_lock().

datapath: Don't call genlmsg_reply() under rcu_read_lock().

genlmsg_reply() indirectly makes a call to kmalloc but takes no
GFP flags, instead using GFP_ATOMIC if in a softirq and GFP_KERNEL
otherwise.  However, here we hold rcu_read_lock(), which requires
GFP_ATOMIC but is not a softirq.  Since we've already built the
reply message, it is safe to release rcu_read_lock(), so do that
before calling genlmsg_reply().

Signed-off-by: Jesse Gross <jesse@nicira.com>
CC: Hao Zheng <hzheng@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>