drivers: wifi: nxp: remove SAP IPv4 address when stopped

Start and stop SAP, the IPv4 address is not removed, if then use STA
mode to connect to EXT-AP with same gateway address as the stopped
SAP, STA will not get the DHCP IPv4 address, as the DHCP offer packet
is dropped due to detect of IPv4 address conflict. Removing SAP IPv4
address when stopped SAP can fix this issue.

Signed-off-by: Maochen Wang <maochen.wang@nxp.com>