fm10k: Reset multicast mode when deleting lport

Deleting lport when multicast mode is configured to
FM10K_XCAST_MODE_ALLMULTI or FM10K_XCAST_MODE_PROMISC will result in
generating orphaned multicast-group entries in the switch manager.
Before deleting the lport, reset multicast mode to FM10K_XCAST_MODE_NONE
to flush out these multicast-group entries.

Signed-off-by: Ngai-Mint Kwan <ngai-mint.kwan@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <Krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>