net/mlx5: fix build on PPC64

net/mlx5: fix build on PPC64

The AltiVec header file breaks boolean type:

error: incompatible types when initializing type
'__vector _bool int' {aka '_vector(4) __bool int'} using type 'int'

If __APPLE_ALTIVEC__ is defined, then bool type is redefined
and conflicts with stdbool.h.

There is no good solution to fix it for the whole project without
breaking something else, so a workaround is inserted in mlx5 PMD.
This workaround is not compatible with C++ but there is no C++ in DPDK.

Suggested-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Suggested-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Tested-by: David Wilder <dwilder@us.ibm.com>
Acked-by: Chao Zhu <chaozhu@linux.vnet.ibm.com>