ISDN: Fix build when CONFIG_ISDN_TTY_FAX is not set

T30_s * is part of a union, so the typedef needs to exist even when
CONFIG_ISDN_TTY_FAX is not set.

include/linux/isdnif.h

@@ -275,7 +275,6 @@ typedef struct setup_parm {
 } setup_parm;
 
 
-#ifdef CONFIG_ISDN_TTY_FAX
 /* T.30 Fax G3 */
 
 #define FAXIDLEN 21
@@ -350,8 +349,6 @@ typedef struct T30_s {
 #define ISDN_FAX_PHASE_D   	4
 #define ISDN_FAX_PHASE_E   	5
 
-#endif /* TTY_FAX */
-
 #define ISDN_FAX_CLASS1_FAE	0
 #define ISDN_FAX_CLASS1_FTS	1
 #define ISDN_FAX_CLASS1_FRS	2