netlabel: correctly list all the static label mappings

[ Upstream commits 0c1233aba1e948c37f6dc7620cb7c253fcd71ce9 and
  a6a8fe950e1b8596bb06f2c89c3a1a4bf2011ba9 ]

When we have a large number of static label mappings that spill across
the netlink message boundary we fail to properly save our state in the
netlink_callback struct which causes us to repeat the same listings.
This patch fixes this problem by saving the state correctly between
calls to the NetLabel static label netlink "dumpit" routines.

Signed-off-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>