I'll list my modifications (keep everything else as it is) here but keep in mind that you most probably want different settings.

See also this post about iPXE in general.

src/config/console.h

(commented in to enable:)

#define    CONSOLE_FRAMEBUFFER /* Graphical framebuffer console */

(changed from us to de:)

#define    KEYBOARD_MAP    de

src/config/general.h

(changed from #undef to #define:)

#define    NET_PROTO_IPV6      /* IPv6 protocol */

(changed from #undef to #define:)

#define    DOWNLOAD_PROTO_HTTPS    /* Secure Hypertext Transfer Protocol */
#define    DOWNLOAD_PROTO_FTP  /* File Transfer Protocol */

(changed from #undef to #define:)

#define    DOWNLOAD_PROTO_NFS  /* Network File System Protocol */

(commented in to disable:)

#undef SANBOOT_PROTO_ISCSI /* iSCSI protocol */
#undef SANBOOT_PROTO_AOE   /* AoE protocol */
#undef SANBOOT_PROTO_IB_SRP    /* Infiniband SCSI RDMA protocol */
#undef SANBOOT_PROTO_FCP   /* Fibre Channel protocol */

(changed from #undef to #define:)

#define    SANBOOT_PROTO_HTTP  /* HTTP SAN protocol */

(commented in to enable - works only for undionly.kpxe:)

#define   IMAGE_ELF       /* ELF image support */

(commented in to enable:)

#define    IMAGE_SCRIPT        /* iPXE script image support */

(commented in to enable - works only for undionly.kpxe:)

#define   IMAGE_COMBOOT       /* SYSLINUX COMBOOT image support */

(commented in to enable:)

#define NSLOOKUP_CMD       /* DNS resolving command */

(commented in to enable:)

#define REBOOT_CMD     /* Reboot command */
#define POWEROFF_CMD       /* Power off command */

(commented in to enable:)

#define PING_CMD       /* Ping command */
#define CONSOLE_CMD        /* Console command */
#define IPSTAT_CMD     /* IP statistics commands */