Clear allocated debug message buffers explicitly

Clear allocated debug message buffers explicitly

When hostapd or wpa_supplicant is run in debug more with key material
prints allowed (-K on the command line), it is possible for passwords
and keying material to show up in debug prints. Since some of the debug
cases end up allocating a temporary buffer from the heap for processing
purposes, a copy of such password may remain in heap. Clear these
temporary buffers explicitly to avoid causing issues for hwsim test
cases that verify contents of memory against unexpected keys.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>