sethdlc: fix host contamination

* Clean INCLUDES to fix the host contamination errors:

  In file included from /usr/src/linux/include/linux/posix_types.h:47:0,
  from /usr/src/linux/include/linux/types.h:17,
  from /usr/src/linux/include/linux/if.h:22,
  from sethdlc.c:23:
  /usr/src/linux/include/asm-generic/posix_types.h:91:3: \
    error: conflicting types for '__kernel_fsid_t'
  } __kernel_fsid_t;
  ^
  .../tmp/sysroots/qemumips/usr/include/asm/posix_types.h:26:3: \
    note: previous declaration of '__kernel_fsid_t' was here
  } __kernel_fsid_t;
  ^

* Correct LIC_FILES_CHKSUM to checkout license infos from sethdl.c
  instead of Makefile.

Signed-off-by: Wenzong Fan <wenzong.fan@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>