The last character of the STA MAC address got replaced with 0x00 due to
truncation if the @1@ macro was used at the end of the URL. Fix this
case by allocating larger buffer for the URL.
Fixes: d4e39c51f8 ("HS 2.0: Move Terms and Conditions Server URL generation from AP to AS")
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>