ipsec-tools: set MACHINE_ARCH, because it depends on kernel

* see:
  http://lists.openembedded.org/pipermail/openembedded-devel/2015-September/103271.html
* fixes:
ERROR: ipsec-tools different signature for task do_configure.sigdata between qemux86copy and qemux86
runtaskdeps changed from ['autoconfautoconf_2.69.bb.do_populate_sysroot:virtual:native', 'automakeautomake_1.15.bb.do_populate_sysroot:virtual:native', 'bisonbison_3.0.4.bb.do_populate_sysroot:virtual:native', 'flexflex_2.5.39.bb.do_populate_sysroot:virtual:native', 'gccgcc-cross_5.2.bb.do_populate_sysroot', 'gccgcc-runtime_5.2.bb.do_populate_sysroot', 'glibcglibc_2.22.bb.do_populate_sysroot', 'gnu-configgnu-config_git.bb.do_populate_sysroot:virtual:native', 'ipsec-toolsipsec-tools_0.8.2.bb.do_patch', 'libtoollibtool-cross_2.4.6.bb.do_populate_sysroot', 'libtoollibtool-native_2.4.6.bb.do_populate_sysroot', 'linuxlinux-yocto_4.1.bb.do_populate_sysroot', 'opensslopenssl_1.0.2d.bb.do_populate_sysroot', 'readlinereadline_6.3.bb.do_populate_sysroot',...