MINOR: build: missing header

MINOR: build: missing header

Regex header file is missing in types/action.h

Repported by Conrad Hoffmann

I cannot build the current dev's master HEAD (ec3c37d) because of this error:

> In file included from include/proto/proto_http.h:26:0,
>                  from src/stick_table.c:26:
> include/types/action.h:102:20: error: field â\80\98reâ\80\99 has incomplete type
>     struct my_regex re;    /* used by replace-header and replace-value */
>                     ^
> Makefile:771: recipe for target 'src/stick_table.o' failed
> make: *** [src/stick_table.o] Error 1

The struct act_rule defined in action.h includes a full struct my_regex
without #include-ing regex.h. Both gcc 5.2.0 and clang 3.6.2 do not allow this.