[iwm] Improve reliability of iwm_release on disassociation a bit.

[ivadasz]

Summary

• We need to first call ivp->iv_newstate(), to enqueue the deauth/deassoc mgmt frame, then flush the tx queue, before actually calling iwm_release().

• cycling a wlan connection via wpa_cli frontend to wpa_supplicant, by issuing disconnect and reconnect commandos works quite well. (There is still an issue when disconnecting/reconnecting to quickly)

• Reassociating or roaming via wpa_supplicant is still broken.

Test Plan

Intel 7260, STA mode

iwm0: <Intel Dual Band Wireless AC 7260> mem 0xf0500000-0xf0501fff irq 17 at device 0.0 on pci2
iwm0: hw rev 0x140, fw ver 16.242414.0, address xx:xx:xx:xx:xx:xx