cxgbe/t4_tom: Demote STALE L2 table entries to RESOLVING in uld_stop.

The STALE state means the L2T entry is valid in hardware but needs to be
refreshed (ARP/NDP) in software. But stop/suspend wipes the hardware
L2T and STALE entries need to be updated just like VALID entries to match
actual hardware state.

Fixes: c1c524852f62 cxgbe/t4_tom: Implement uld_stop and uld_restart for ULD_TOM.
MFC after: 1 week
Sponsored by: Chelsio Communications