node: fix arm64 build with old gcc

node: fix arm64 build with old gcc

Older GCC(~4) complains about uninitialized 'dip'
var though all the lanes of the vec register are set.
Hence this patch explicitly initializes vec register
to fix the issue.

In file included from ip4_lookup.c:34:0:
ip4_lookup_neon.h: n function ‘ip4_lookup_node_process’: \
ip4_lookup_neon.h:25:12: error: ‘dip’ may be used uninitialized in \
	this function [-Werror=maybe-uninitialized]
  int32x4_t dip;
            ^

Fixes: 16df6a2c6671 ("node: add IPv4 lookup for arm64")

Reported-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Nithin Dabilpuram <ndabilpuram@marvell.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Jerin Jacob <jerinj@marvell.com>