net/mlx5e: always initialize frag->last_in_page

The commit 069d1146 ("net/mlx5e: RX, Enhance legacy Receive Queue
memory scheme") introduced an undefined behaviour below due to
"frag->last_in_page" is only initialized in mlx5e_init_frags_partition()
when,

if (next_frag.offset + frag_info[f].frag_stride > PAGE_SIZE)

or after bailed out the loop,

for (i = 0; i < mlx5_wq_cyc_get_size(&rq->wqe.wq); i++)

As the result, there could be some "frag" have uninitialized
value of "last_in_page".

Later, get_frag() obtains those "frag" and check "frag->last_in_page" in
mlx5e_put_rx_frag() and triggers the error during boot. Fix it by always
initializing "frag->last_in_page" to "false" in
mlx5e_init_frags_partition().

UBSAN: Undefined behaviour in
drivers/net/ethernet/mellanox/mlx5/core/en_rx.c:325:12
load of value 170 is not a valid value for type 'bool' (aka '_Bool')
Call trace:
 dump_backtrace+0x0/0x264
 show_stack+0x20/0x2c
 dump_stack+0xb0/0x104
 __ubsan_handle_load_invalid_value+0x104/0x128
 mlx5e_handle_rx_cqe+0x8e8/0x12cc [mlx5_core]
 mlx5e_poll_rx_cq+0xca8/0x1a94 [mlx5_core]
 mlx5e_napi_poll+0x17c/0xa30 [mlx5_core]
 net_rx_action+0x248/0x940
 __do_softirq+0x350/0x7b8
 irq_exit+0x200/0x26c
 __handle_domain_irq+0xc8/0x128
 gic_handle_irq+0x138/0x228
 el1_irq+0xb8/0x140
 arch_cpu_idle+0x1a4/0x348
 do_idle+0x114/0x1b0
 cpu_startup_entry+0x24/0x28
 rest_init+0x1ac/0x1dc
 arch_call_rest_init+0x10/0x18
 start_kernel+0x4d4/0x57c

Fixes: 069d1146 ("net/mlx5e: RX, Enhance legacy Receive Queue memory scheme")
Signed-off-by: Qian Cai <cai@lca.pw>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx5/core/en_main.c

@@ -331,12 +331,11 @@ static inline u64 mlx5e_get_mpwqe_offset(struct mlx5e_rq *rq, u16 wqe_ix)
 
 static void mlx5e_init_frags_partition(struct mlx5e_rq *rq)
 {
-	struct mlx5e_wqe_frag_info next_frag, *prev;
+	struct mlx5e_wqe_frag_info next_frag = {};
+	struct mlx5e_wqe_frag_info *prev = NULL;
 	int i;
 
 	next_frag.di = &rq->wqe.di[0];
-	next_frag.offset = 0;
-	prev = NULL;
 
 	for (i = 0; i < mlx5_wq_cyc_get_size(&rq->wqe.wq); i++) {
 		struct mlx5e_rq_frag_info *frag_info = &rq->wqe.info.arr[0];