bnxt_en: Refactor bnxt_close_nic().

bnxt_en: Refactor bnxt_close_nic().

Orabug: 27648355, 27648339

Add a new __bnxt_close_nic() function to do all the work previously done
in bnxt_close_nic() except waiting for SRIOV configuration.  The new
function will be used in the next patch as part of SRIOV cleanup.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 86e953db0114f396f916344395160aa267bf2627)
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>
Conflicts:
	drivers/net/ethernet/broadcom/bnxt/bnxt.c