BUILD: spoe: fix build warning on older gcc around sub-struct initialization

BUILD: spoe: fix build warning on older gcc around sub-struct initialization

gcc-4.8 is unhappy with the cfg_file initialization:

  src/flt_spoe.c: In function 'parse_spoe_flt':
  src/flt_spoe.c:2202:9: warning: missing braces around initializer [-Wmissing-braces]
    struct cfgfile      cfg_file = {0};
         ^
  src/flt_spoe.c:2202:9: warning: (near initialization for 'cfg_file.list') [-Wmissing-braces]

This is due to the embedded list member. Initializing it to empty like
we do almost everywhere else makes it happy. No backport is needed as
this was changed in 3.1-dev5 only.