10-RC unable to build kernel without INET (i.e. IPv6-only)

Under 9.2 the following could be used to build an IPv6-only kernel:

/sys/amd64/conf/TEST :

include GENERIC
makeoptions   MKMODULESENV+="WITHOUT_INET_SUPPORT="
nooptions   INET


Now with stable/10 the:

  make buildkernel KERNCONF=TEST

fails while building xen support:

[...]
cc  -c -O2 -pipe -fno-strict-aliasing  -std=c99 -g -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes  -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual  -
Wundef -Wno-pointer-sign -fformat-extensions  -Wmissing-include-dirs -fdiagnostics-show-option  -Wno-error-tautological-compare -Wno-error-empty-body  -Wno-error-
parentheses-equality  -nostdinc  -I. -I/usr/src/sys -I/usr/src/sys/contrib/altq -I/usr/src/sys/contrib/libfdt -D_KERNEL -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h  
-fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -mno-aes -mno-avx -mcmodel=kernel -mno-red-zone -mno-mmx -mno-sse -msoft-float  -fno-asynchronous-unwind-
tables -ffreestanding -fstack-protector -Werror  /usr/src/sys/dev/xen/control/control.c
ctfconvert -L VERSION -g control.o
cc  -c -O2 -pipe -fno-strict-aliasing  -std=c99 -g -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes  -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual  -
Wundef -Wno-pointer-sign -fformat-extensions  -Wmissing-include-dirs -fdiagnostics-show-option  -Wno-error-tautological-compare -Wno-error-empty-body  -Wno-error-
parentheses-equality  -nostdinc  -I. -I/usr/src/sys -I/usr/src/sys/contrib/altq -I/usr/src/sys/contrib/libfdt -D_KERNEL -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h  
-fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -mno-aes -mno-avx -mcmodel=kernel -mno-red-zone -mno-mmx -mno-sse -msoft-float  -fno-asynchronous-unwind-
tables -ffreestanding -fstack-protector -Werror  /usr/src/sys/dev/xen/netback/netback.c
/usr/src/sys/dev/xen/netback/netback.c:2244:8: error: use of undeclared identifier 'ifr'
                        if (ifr->ifr_reqcap & IFCAP_TXCSUM) {
                            ^
/usr/src/sys/dev/xen/netback/netback.c:2251:9: error: use of undeclared identifier 'ifr'
                        if ((ifr->ifr_reqcap & IFCAP_RXCSUM)) {
                             ^
/usr/src/sys/dev/xen/netback/netback.c:2284:18: error: use of undeclared identifier 'ifr'
                        ifp->if_mtu = ifr->ifr_mtu;
                                      ^
/usr/src/sys/dev/xen/netback/netback.c:2292:31: error: use of undeclared identifier 'ifr'
                        error = ifmedia_ioctl(ifp, ifr, &xnb->sc_media, cmd);
                                                   ^
4 errors generated.
*** Error code 1

Stop.
make[2]: stopped in /usr/obj/usr/src/sys/TEST
*** Error code 1



  Mark