MINOR: proxy/checks: Move parsing of httpchk option in checks.c

Parsing of the proxy directive "option httpchk" have been moved in checks.c.
diff --git a/include/proto/checks.h b/include/proto/checks.h
index 4dba34a..cc0ab0b 100644
--- a/include/proto/checks.h
+++ b/include/proto/checks.h
@@ -83,6 +83,8 @@
 			       const char *file, int line);
 int proxy_parse_spop_check_opt(char **args, int cur_arg, struct proxy *curpx, struct proxy *defpx,
 			       const char *file, int line);
+int proxy_parse_httpchk_opt(char **args, int cur_arg, struct proxy *curpx, struct proxy *defpx,
+			    const char *file, int line);
 
 int set_srv_agent_send(struct server *srv, const char *send);