mem: skip attaching external memory in secondary process

mem: skip attaching external memory in secondary process

Currently, EAL init in secondary processes will attach all fbarrays
in the memconfig to have access to the primary process's page tables.
However, fbarrays corresponding to external memory segments should
not be attached at initialization, because this will happen as part
of `rte_extmem_attach` [1] or `rte_malloc_heap_memory_attach` [2] calls.

1: https://doc.dpdk.org/api/rte__memory_8h.html#a2796da68de6825f8edf53759f8e4d230
2: https://doc.dpdk.org/api/rte__malloc_8h.html#af6360dea35bdf162feeb2b62cf149fd3

Fixes: ff3619d6244b ("malloc: allow attaching to external memory chunks")
Cc: stable@dpdk.org
Suggested-by: Anatoly Burakov <anatoly.burakov@intel.com>
Signed-off-by: Deepak Khandelwal <deepak.khandelwal@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>