net/ixgbe: fix build with gcc 4.8.5

net/ixgbe: fix build with gcc 4.8.5

Build error:
  In function ‘ixgbe_recv_pkts_lro_bulk_alloc’:
../drivers/net/ixgbe/ixgbe_rxtx.c:2209:24:
  error: ‘next_sc_entry’ may be used uninitialized in this function
  [-Werror=maybe-uninitialized]
    next_sc_entry->fbuf = first_seg;
                        ^
http://mails.dpdk.org/archives/test-report/2020-January/113891.html

This is a compiler false positive and error not seen by newer compilers,
or clang but to fix the warning initializing the complained variable.

According git bisect, no idea how:
Fixes: ad43b7bce95b ("net/ixgbe: avoid multiple definitions of bool")
Reported-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Tested-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Xiaolong Ye <xiaolong.ye@intel.com>