acinclude: Transparent checking for DPDK dependencies.

acinclude: Transparent checking for DPDK dependencies.

'AC_CHECK_DECL' makes almost same thing as 'AC_COMPILE_IFELSE', but
looks more pretty. Additionally it prints checking results in a
user-visible way making it easy to understand which configs checked
and why we need one or another dependency.

For exmaple, with this patch, configure log may look like this:

  checking whether dpdk datapath is enabled... yes
  checking for rte_config.h... yes
  checking whether RTE_LIBRTE_VHOST_NUMA is declared... no
  checking whether RTE_EAL_NUMA_AWARE_HUGEPAGES is declared... yes
  checking for library containing get_mempolicy... -lnuma
  checking whether RTE_LIBRTE_VHOST_NUMA is declared... (cached) no
  checking whether RTE_LIBRTE_PMD_PCAP is declared... yes
  checking for library containing pcap_dump... -lpcap
  checking whether RTE_LIBRTE_PDUMP is declared... yes
  checking whether RTE_LIBRTE_MLX5_PMD is declared... no
  checking whether RTE_LIBRTE_MLX4_PMD is declared... yes
  checking whether RTE_LIBRTE_MLX4_DLOPEN_DEPS is declared... yes

Instead of just:

  checking whether dpdk datapath is enabled... yes
  checking for rte_config.h... yes
  checking for library containing get_mempolicy... -lnuma
  checking for library containing pcap_dump... -lpcap

Anyway, code looks more clean and easier to understand. Also, with
this change we're defining VHOST_NUMA only if RTE_LIBRTE_VHOST_NUMA
defined. This costs nothing as all the checks with 'AC_CHECK_DECL'
are cached.

Acked-by: Flavio Leitner <fbl@sysclose.org>
Acked-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>