filter: Fix the match() filter grammar

In the filter_re rule, the match() filter's grammar was written with a
":" at the start of the line instead of a "|", therefore yacc did not
consider it part of the rule. This patch corrects that.

Reported-by: Andras Mitzki <micek@balabit.hu>
Signed-off-by: Gergely Nagy <algernon@balabit.hu>