Hi Peter,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on bpf-next/master]

url:    https://github.com/0day-ci/linux/commits/Peter-Oskolkov/bpf-add-BPF_LWT_ENCAP_IP-option-to-bpf_lwt_push_encap/20190207-205725
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: m68k-sun3_defconfig (attached as .config)
compiler: m68k-linux-gnu-gcc (Debian 8.2.0-11) 8.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=8.2.0 make.cross ARCH=m68k 

All errors (new ones prefixed by >>):

   m68k-linux-gnu-ld: drivers/rtc/proc.o: in function `is_rtc_hctosys.isra.0':
   proc.c:(.text+0x178): undefined reference to `strcmp'
   m68k-linux-gnu-ld: net/core/lwt_bpf.o: in function `bpf_lwt_xmit_reroute':

quoted

lwt_bpf.c:(.text+0x256): undefined reference to `ip6_route_output_flags'

   m68k-linux-gnu-ld: net/core/lwt_bpf.o: in function `bpf_input':

quoted

lwt_bpf.c:(.text+0x836): undefined reference to `ip6_route_input'

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