eal/linux: fix build error on RHEL 7.6

eal/linux: fix build error on RHEL 7.6

Previous fix gives hiccups to gcc on RHEL 7.6:

== Build lib/librte_eal/linux/eal
  CC eal_interrupts.o
...lib/librte_eal/linux/eal/eal_interrupts.c: In function
  ‘eal_intr_thread_main’:
...lib/librte_eal/linux/eal/eal_interrupts.c:1048:9: error: missing
  initializer for field ‘events’ of ‘struct epoll_event’
  [-Werror=missing-field-initializers]
  struct epoll_event ev = { };
         ^
In file included from ...lib/librte_eal/linux/eal/eal_interrupts.c:15:0:
/usr/include/sys/epoll.h:89:12: note: ‘events’ declared here
   uint32_t events; /* Epoll events */
            ^
...lib/librte_eal/linux/eal/eal_interrupts.c: At top level:
cc1: error: unrecognized command line option
  "-Wno-address-of-packed-member" [-Werror]
cc1: all warnings being treated as errors

Fixes: e0ab8020ac2a ("eal/linux: fix uninitialized data valgrind warning")
Cc: stable@dpdk.org
Reported-by: Andrew Rybchenko <arybchenko@solarflare.com>
Signed-off-by: David Marchand <david.marchand@redhat.com>