Code cleanup: Rename enum -> enum filterflags

Code cleanup: Rename enum -> enum filterflags

Bit mask ints are better to make enums as GDB already has support to
automatically decode them:

before this patch:
	(gdb) p filterflags
	$1 = 51
	(gdb) p/x filterflags
	$2 = 0x33

after this patch:
	(gdb) p filterflags
	$1 = (COREFILTER_ANON_PRIVATE | COREFILTER_ANON_SHARED | COREFILTER_ELF_HEADERS | COREFILTER_HUGETLB_PRIVATE)

gdb/ChangeLog
2015-06-15  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* linux-tdep.c (enum filterflags): Make it from anonymous enum.
	(dump_mapping_p): Use it for parameter filterflags.
	(linux_find_memory_regions_full): Use it for variable filterflags.