wifi: wfx: fix memory leak when starting AP

In the Linux kernel, the following vulnerability has been resolved:

wifi: wfx: fix memory leak when starting AP

Kmemleak reported this error:

unreferenced object 0xd73d1180 (size 184):
comm "wpa_supplicant", pid 1559, jiffies 13006305 (age 964.245s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 1e 00 01 00 00 00 00 00 ................
backtrace:
[<5ca11420>] kmem_cache_alloc+0x20c/0x5ac
[<127bdd74>] __alloc_skb+0x144/0x170
[<fb8a5e38>] __netdev_alloc_skb+0x50/0x180
[<0f9fa1d5>] __ieee80211_beacon_get+0x290/0x4d4 [mac80211]
[<7accd02d>] ieee80211_beacon_get_tim+0x54/0x18c [mac80211]
[<41e25cc3>] wfx_start_ap+0xc8/0x234 [wfx]
[<93a70356>] ieee80211_start_ap+0x404/0x6b4 [mac80211]
[<a4a661cd>] nl80211_start_ap+0x76c/0x9e0 [cfg80211]
[<47bd8b68>] genl_rcv_msg+0x198/0x378
[<453ef796>] netlink_rcv_skb+0xd0/0x130
[<6b7c977a>] genl_rcv+0x34/0x44
[<66b2d04d>] netlink_unicast+0x1b4/0x258
[<f965b9b6>] netlink_sendmsg+0x1e8/0x428
[<aadb8231>] ____sys_sendmsg+0x1e0/0x274
[<d2b5212d>] ___sys_sendmsg+0x80/0xb4
[<69954f45>] __sys_sendmsg+0x64/0xa8
unreferenced object 0xce087000 (size 1024):
comm "wpa_supplicant", pid 1559, jiffies 13006305 (age 964.246s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
10 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00 ...@............
backtrace:
[<9a993714>] __kmalloc_track_caller+0x230/0x600
[<f83ea192>] kmalloc_reserve.constprop.0+0x30/0x74
[<a2c61343>] __alloc_skb+0xa0/0x170
[<fb8a5e38>] __netdev_alloc_skb+0x50/0x180
[<0f9fa1d5>] __ieee80211_beacon_get+0x290/0x4d4 [mac80211]
[<7accd02d>] ieee80211_beacon_get_tim+0x54/0x18c [mac80211]
[<41e25cc3>] wfx_start_ap+0xc8/0x234 [wfx]
[<93a70356>] ieee80211_start_ap+0x404/0x6b4 [mac80211]
[<a4a661cd>] nl80211_start_ap+0x76c/0x9e0 [cfg80211]
[<47bd8b68>] genl_rcv_msg+0x198/0x378
[<453ef796>] netlink_rcv_skb+0xd0/0x130
[<6b7c977a>] genl_rcv+0x34/0x44
[<66b2d04d>] netlink_unicast+0x1b4/0x258
[<f965b9b6>] netlink_sendmsg+0x1e8/0x428
[<aadb8231>] ____sys_sendmsg+0x1e0/0x274
[<d2b5212d>] ___sys_sendmsg+0x80/0xb4

However, since the kernel is build optimized, it seems the stack is not
accurate. It appears the issue is related to wfx_set_mfp_ap(). The issue
is obvious in this function: memory allocated by ieee80211_beacon_get()
is never released. Fixing this leak makes kmemleak happy.