mwifiex: Fix possible buffer overflows in mwifiex_cmd_append_vsie_tlv()

commit b70261a288ea4d2f4ac7cd04be08a9f0f2de4f4d upstream.

mwifiex_cmd_append_vsie_tlv() calls memcpy() without checking
the destination size may trigger a buffer overflower,
which a local user could use to cause denial of service
or the execution of arbitrary code.
Fix it by putting the length check before calling memcpy().

Signed-off-by: Qing Xu <m1s5p6688@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
[bwh: Backported to 3.16:
 - Use dev_info() instead of mwifiex_dbg()
 - Adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>