Can't build #5

Can't build netmap-ipfw on FreeBSD 11
$ cd ~/src
[mystical@imslu ~/src]$ freebsd-version
11.0-RELEASE-p1
[mystical@imslu ~/src]$ git clone https://github.com/luigirizzo/netmap-ipfw.git
[mystical@imslu ~/src]$ git clone https://github.com/luigirizzo/netmap.git

[mystical@imslu ~/src/netmap-ipfw]$ make NETMAP_INC=../netmap/sys
gmake
gmake[1]: Entering directory '/usr/home/mystical/src/netmap-ipfw'
Building userspace ...
gmake[2]: Entering directory '/usr/home/mystical/src/netmap-ipfw/ipfw'
(cd ../objs; gmake -f ../Makefile.kipfw include_e)
gmake[3]: Entering directory '/usr/home/mystical/src/netmap-ipfw/objs'
Building /usr/home/mystical/src/netmap-ipfw/objs/../objs/include_e ...
gmake[3]: Leaving directory '/usr/home/mystical/src/netmap-ipfw/objs'
CC ipfw2.c
ipfw2.c:2856:19: error: shifting a negative signed value is undefined [-Werror,-Wshift-negative-value]
d[1] = htonl(~0 << (32 - 24));
~~ ^
/usr/include/netinet/in.h:117:26: note: expanded from macro 'htonl'
#define htonl(x) __htonl(x)
^
....
Too many errors
...
7 errors generated.
gmake[2]: *** [../Makefile.inc:28: ipfw2.o] Error 1
gmake[2]: Leaving directory '/usr/home/mystical/src/netmap-ipfw/ipfw'
gmake[1]: *** [Makefile:17: ipfw] Error 2
gmake[1]: Leaving directory '/usr/home/mystical/src/netmap-ipfw'
*** Error code 2

Stop.
make: stopped in /usr/home/mystical/src/netmap-ipfw

[mystical@imslu ~/src/netmap-ipfw]$ make NETMAP_INC=/usr/src/sys
gmake
gmake[1]: Entering directory '/usr/home/mystical/src/netmap-ipfw'
Building userspace ...
gmake[2]: Entering directory '/usr/home/mystical/src/netmap-ipfw/ipfw'
CC ipfw2.c
ipfw2.c:2856:19: error: shifting a negative signed value is undefined [-Werror,-Wshift-negative-value]
d[1] = htonl(~0 << (32 - 24));
~~ ^
/usr/include/netinet/in.h:117:26: note: expanded from macro 'htonl'
#define htonl(x) __htonl(x)
^
....
Too many errors

I tried to compile only kipfw:
[mystical@imslu ~/src/netmap-ipfw]$ make NETMAP_INC=/usr/src/sys
gmake
gmake[1]: Entering directory '/usr/home/mystical/src/netmap-ipfw'
Building datapath ...
gmake[2]: Entering directory '/usr/home/mystical/src/netmap-ipfw/objs'
CC ../sys/netpfil/ipfw/ip_fw2.c
In file included from :316:
In file included from :12:
/usr/home/mystical/src/netmap-ipfw/objs/../extra/glue.h:397:18: error: redefinition of typedef 'u_register_t' is a C11 feature [-Werror,-Wtypedef-redefinition]
typedef uint64_t u_register_t; // XXX not on osx ?
^
/usr/src/sys/sys/types.h:228:24: note: previous definition is here
typedef __u_register_t u_register_t;
^

[mystical@imslu ~/src/netmap-ipfw]$ make NETMAP_INC=../netmap/sys
gmake
gmake[1]: Entering directory '/usr/home/mystical/src/netmap-ipfw'
Building datapath ...
gmake[2]: Entering directory '/usr/home/mystical/src/netmap-ipfw/objs'
CC ../sys/netpfil/ipfw/ip_fw2.c
In file included from ../sys/netpfil/ipfw/ip_fw2.c:58:
In file included from /usr/include/sys/socketvar.h:43:
In file included from /usr/include/sys/sockbuf.h:39:
/usr/include/sys/_task.h:47:8: error: redefinition of 'task'
struct task {
^
../extra/sys/sys/taskqueue.h:16:8: note: previous definition is here
struct task {
^