Fix hostapd BSS_TM_REQ handling of bss_term parameter

Fix hostapd BSS_TM_REQ handling of bss_term parameter

The TSF field in BSS termination information was not cleared correctly.
It was supposed to be cleared to all zeros, but the memset call did not
point at offset 2; instead, it cleared it with 0x02 octets and also
cleared the subelement header with 0x02 octets while leaving two last
octets uninitialized.

Fixes: a30dff07fb18 ("Add BSS_TM_REQ command to send BSS Transition Management Request")
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>