eal: fix out of bound access when no CPU available

eal: fix out of bound access when no CPU available

In the unlikely case when the dpdk application is started with no cpu
available in the [0, RTE_MAX_LCORE - 1] range, the master_lcore is
automatically chosen as RTE_MAX_LCORE which triggers an out of bound
access.

Either you have a crash then, or the initialisation fails later when
trying to pin the master thread on it.
In my test, with RTE_MAX_LCORE == 2:

$ taskset -c 2 ./master/app/testpmd --no-huge -m 512 --log-level *:debug
[...]
EAL: pthread_setaffinity_np failed
PANIC in eal_thread_init_master():
cannot set affinity
7: [./master/app/testpmd() [0x47f629]]

Bugzilla ID: 19
Fixes: 2eba8d21f3c9 ("eal: restrict cores auto detection")
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>