mesh: Fix crash on removing virtual mesh interface

mesh: Fix crash on removing virtual mesh interface

If a virtual mesh interface has been created and is still operational
when the main interface is removed (e.g., Wi-Fi hardware ejected), the
following crash occurred with the below backtrace:

WPA_TRACE: eloop SIGSEGV - START
[1]: /usr/local/sbin/wpa_supplicant() [0x44ef7e]
     eloop_sigsegv_handler() home/saurav/hostap/wpa_supplicant/../src/utils/eloop.c:123
[2]: /lib/x86_64-linux-gnu/libc.so.6(+0x36d40) [0x7f4c395cfd40]
[3]: /usr/local/sbin/wpa_supplicant(wpa_supplicant_remove_iface+0xd0) [0x57f500]
     wpa_supplicant_remove_iface() home/saurav/hostap/wpa_supplicant/wpa_supplicant.c:5338
[4]: /usr/local/sbin/wpa_supplicant() [0x57fbef]
     wpa_supplicant_deinit_iface() home/saurav/hostap/wpa_supplicant/wpa_supplicant.c:5069
[5]: /usr/local/sbin/wpa_supplicant(wpa_supplicant_remove_iface+0xc5) [0x57f4f5]
     wpa_supplicant_remove_iface() home/saurav/hostap/wpa_supplicant/wpa_supplicant.c:5343
[6]: /usr/local/sbin/wpa_supplicant(wpas_dbus_handler_remove_interface+0x8d) [0x55baad]
     wpas_dbus_handler_remove_interface() home/saurav/hostap/wpa_supplicant/dbus/dbus_new_handlers.c:679
[7]: /usr/local/sbin/wpa_supplicant() [0x5560cb]
     msg_method_handler() home/saurav/hostap/wpa_supplicant/dbus/dbus_new_helpers.c:354
     message_handler() home/saurav/hostap/wpa_supplicant/dbus/dbus_new_helpers.c:410
[8]: /lib/x86_64-linux-gnu/libdbus-1.so.3(+0x1be86) [0x7f4c39979e86]
[9]: /lib/x86_64-linux-gnu/libdbus-1.so.3(dbus_connection_dispatch+0x381) [0x7f4c3996ca21]
[10]: /usr/local/sbin/wpa_supplicant() [0x567148]
     dispatch_data() home/saurav/hostap/wpa_supplicant/dbus/dbus_common.c:36
[11]: /usr/local/sbin/wpa_supplicant() [0x5674a7]
     process_watch() home/saurav/hostap/wpa_supplicant/dbus/dbus_common.c:75
     process_watch_read() home/saurav/hostap/wpa_supplicant/dbus/dbus_common.c:90
[12]: /usr/local/sbin/wpa_supplicant() [0x44f297]
     eloop_sock_table_dispatch() home/saurav/hostap/wpa_supplicant/../src/utils/eloop.c:598
[13]: /usr/local/sbin/wpa_supplicant(eloop_run+0x1fe) [0x44ff1e]
     eloop_run() home/saurav/hostap/wpa_supplicant/../src/utils/eloop.c:1219
[14]: /usr/local/sbin/wpa_supplicant(wpa_supplicant_run+0x77) [0x57fd87]
     wpa_supplicant_run() home/saurav/hostap/wpa_supplicant/wpa_supplicant.c:5608
[15]: /usr/local/sbin/wpa_supplicant(main+0x3a8) [0x43ba88]
     main() home/saurav/hostap/wpa_supplicant/main.c:392
WPA_TRACE: eloop SIGSEGV - END
Aborted (core dumped)

Signed-off-by: Saurav Babu <saurav.babu@samsung.com>