lib: rename enum to avoid conflict

lib: rename enum to avoid conflict

Two different definitions of "enum filter_type" exist in libfrr:
one in lib/filter.h and other in lib/command_match.h. Rename one
of them to resolve a conflict that happens when both headers are
included by the same file.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>