net: sh_eth: Fix missing rtnl lock in suspend/resume path

Fix the suspend/resume path by ensuring the rtnl lock is held where
required. Calls to sh_eth_close, sh_eth_open and wol operations must be
performed under the rtnl lock to prevent conflicts with ongoing ndo
operations.

Fixes: b71af046 ("sh_eth: add more PM methods")
Tested-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>