Compiling with clang and -Wundef makes the compiler report a usage of
undefined PF_MAX macro in security/selinux/include/classmap.h:

    In file included from scripts/selinux/mdp/mdp.c:48:
    security/selinux/include/classmap.h:37:31: warning: no previous
    extern declaration for non-static variable 'secclass_map'
    [-Wmissing-variable-declarations]
    struct security_class_mapping secclass_map[] = {
                                  ^
    security/selinux/include/classmap.h:235:5: error: 'PF_MAX' is not
    defined, evaluates to 0 [-Werror,-Wundef]
    #if PF_MAX > 43
        ^
    In file included from scripts/selinux/genheaders/genheaders.c:17:
    security/selinux/include/classmap.h:37:31: warning: no previous
    extern declaration for non-static variable 'secclass_map'
    [-Wmissing-variable-declarations]
    struct security_class_mapping secclass_map[] = {
                                  ^
    security/selinux/include/classmap.h:235:5: error: 'PF_MAX' is not
    defined, evaluates to 0 [-Werror,-Wundef]
    #if PF_MAX > 43
        ^

PF_MAX is defined in include/linux/socket.h but not in
include/uapi/linux/socket.h. Therefore host programs have to rely on the
definition from libc's /usr/include/bits/socket.h, included by
<sys/socket.h>.

Fix the issue by using sys/socket.h in mdp and genheaders. When
classmap.h is included by security/selinux/avc.c, it uses the kernel
definition of PF_MAX, which makes the test consistent.

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>