config: add static linkage of mlx dependency

config: add static linkage of mlx dependency

The libraries provided by rdma-core may be statically linked
if enabling CONFIG_RTE_IBVERBS_LINK_STATIC in the make-based build.
If CONFIG_RTE_BUILD_SHARED_LIB is disabled, the applications
will embed the mlx PMDs with ibverbs and the mlx libraries.
If CONFIG_RTE_BUILD_SHARED_LIB is enabled,
the mlx PMDs will embed ibverbs and the mlx libraries.

Support with meson may be added later.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Shahaf Shuler <shahafs@mellanox.com>