net: Fix typo in comment about ancillary data

Ingo sent typo fixes for tools/ and this resulted in a warning when
building the perf/core branch that will be sent upstream in the next
merge window:

  Warning: Kernel ABI header at 'tools/perf/trace/beauty/include/linux/socket.h' differs from latest version at 'include/linux/socket.h'
  diff -u tools/perf/trace/beauty/include/linux/socket.h include/linux/socket.h

Fix the typo on the kernel file to address this.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>