malloc: fix finding maximum contiguous IOVA size

malloc: fix finding maximum contiguous IOVA size

malloc_elem_find_max_iova_contig() could return invalid size due to a
missing sanity check. The following gdb output shows how 'cur_size' can be
invalid in find_biggest_element().

	(gdb) p/x cur_size
	$4 = 0xffffffffffe42900
	(gdb) p elem
	$1 = (struct malloc_elem *) 0x12e842000
	(gdb) p *elem
	$2 = {heap = 0x7ffff7ff387c, prev = 0x12e831fc0, next =
		0x12e842900, free_list = {le_next = 0x109538000, le_prev =
		0x7ffff7ff3894}, msl = 0x7ffff7ff107c, state = ELEM_FREE,
		pad = 0, size = 2304}
	(gdb) p *elem->msl
	$5 = {{base_va = 0x100200000, addr_64 = 4297064448}, page_sz =
		2097152, socket_id = 0, version = 790, len = 17179869184,
		external = 0, memseg_arr = {name = "memseg-2048k-0-0",
		'\000' <repeats 47 times>, count = 493, len = 8192, elt_sz
		= 48, data = 0x10002e000, rwlock = {cnt = 0}}}

Fixes: 9fe6bceafd51 ("malloc: add finding biggest free IOVA-contiguous element")
Cc: stable@dpdk.org
Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>