vppinfra: fix u32x4_byte_swap on Arm

vppinfra: fix u32x4_byte_swap on Arm

Fix the endianness conversion function u32x4_byte_swap() on Arm. Here's
an example of using this function with and without the fix.

This issue is seen using Mellanox NIC RDMA driver on Arm servers.
The packet length cannot be parsed correctly.

Testing code:
u32x4 s = {0x12345678, 0x23456789, 0x3456789a, 0x456789ab};
u32x4 ss = u32x4_byte_swap (s);

Without the code change:
(gdb) p /x s
$1 = {0x12345678, 0x23456789, 0x3456789a, 0x456789ab}
(gdb) p /x ss
$2 = {0x23456789, 0x12345678, 0x456789ab, 0x3456789a}

With the code change:
(gdb) p /x s
$3 = {0x12345678, 0x23456789, 0x3456789a, 0x456789ab}
(gdb) p /x ss
$4 = {0x78563412, 0x89674523, 0x9a785634, 0xab896745}

Type: fix

Change-Id: Ie5f263e94331783940e7c00397092a64e4fc4279
Signed-off-by: Lijian Zhang <Lijian.Zhang@arm.com>
Reviewed-by: Jieqiang Wang <Jieqiang.Wang@arm.com>
Reviewed-by: Govindarajan Mohandoss <Govindarajan.Mohandoss@arm.com>