tethering: Fix use after free

Methods of reproducing:

in loop
1) connmanctl tether wifi on my_ssid my_pasword
2) conencting client
3) connmanctl tether wifi off

con[14819.539062] tether: port 1(wlan0) entered disabled state
nmand2[3831]: ../git/src/technology.c:set_property() property Tethering
connmand2[3831]: ../git/plugins/wifi.c:tech_set_tethering()
connmand2[3831]: ../git/src/technology.c:connman_technology_tethering_notify() technology 0xb57006e0 enabled 0
connmand2[3831]: ../git/src/tethering.c:__connman_tethering_set_disabled() enabled 0
=================================================================
==3831==ERROR: AddressSanitizer: heap-use-after-free on address 0xb490c370 at pc 0x41c2e9c0 bp 0xbedf7494 sp 0xbedf7060
READ of size 2 at 0xb490c370 thread T0
    #0 0x41c2e9bf  (/usr/lib/libasan.so.5+0x41c2e9bf)

0xb490c370 is located 0 bytes inside of 18-byte region [0xb490c370,0xb490c382)
freed by thread T0 here:
    #0 0x41c73ee7 in free (/usr/lib/libasan.so.5+0x41c73ee7)
    #1 0x42877473  (/usr/lib/libglib-2.0.so.0+0x42877473)

previously allocated by thread T0 here:
    #0 0x41c7421b in malloc (/usr/lib/libasan.so.5+0x41c7421b)
    #1 0x42890b8b in g_malloc (/usr/lib/libglib-2.0.so.0+0x42890b8b)
    sailfishos#2 0x9d3a7 in sta_authorized ../git/plugins/wifi.c:3004
    sailfishos#3 0xa79eb in callback_sta_authorized ../git/gsupplicant/supplicant.c:626
    sailfishos#4 0xc3dd7 in signal_sta_authorized ../git/gsupplicant/supplicant.c:2779
    sailfishos#5 0xceb2f in g_supplicant_filter ../git/gsupplicant/supplicant.c:3620
    sailfishos#6 0x419fb123 in dbus_connection_dispatch (/usr/lib/libdbus-1.so.3+0x419fb123)
    sailfishos#7 0xb2501d17  (<unknown module>)

SUMMARY: AddressSanitizer: heap-use-after-free (/usr/lib/libasan.so.5+0x41c2e9bf)
Shadow bytes around the buggy address:
  0x36921810: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x36921820: fa fa fa fa fa fa fa fa fa fa fa fa fd fd fd fd
  0x36921830: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x36921840: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x36921850: fa fa fa fa fa fa 00 00 00 fa fa fa fa fa fa fa
=>0x36921860: fa fa 00 00 00 00 fa fa fa fa fa fa fa fa[fd]fd
  0x36921870: fd fa fa fa 00 00 00 00 fa fa fa fa fa fa fa fa
  0x36921880: fa fa fa fa fa fa 00 00 00 04 fa fa fa fa fa fa
  0x36921890: fa fa fa fa fa fa fa fa fd fd fd fd fa fa fa fa
  0x369218a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x369218b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==3831==ABORTING

(cherry picked from commit 799334d)

connman/src/tethering.c

@@ -638,8 +638,8 @@ void __connman_tethering_client_register(const char *addr)
 
 void __connman_tethering_client_unregister(const char *addr)
 {
-	g_hash_table_remove(clients_table, addr);
 	client_removed(addr);
+	g_hash_table_remove(clients_table, addr);
 }
 
 int __connman_tethering_init(void)