Fix warning inside comment

Signed-off-by: Gilles Espinasse <g.esp@free.fr>

Fix this warning seen with -Wall
libnet_if_addr.c:277:1: warning: "/*" within comment
libnet: update for obsolete INCLUDE directive

Signed-off-by: Gilles Espinasse <g.esp@free.fr>

Using autoreconf (with automake-1.12.6) show those warnings

autoreconf: running: automake --add-missing --copy --force-missing
Makefile.am.common:14: warning: 'INCLUDES' is the old name for 'AM_CPPFLAGS' (or '*_CPPFLAGS')
Makefile.am:9:   'Makefile.am.common' included from here
Makefile.am.common:14: warning: 'INCLUDES' is the old name for 'AM_CPPFLAGS' (or '*_CPPFLAGS')
include/Makefile.am:3:   'Makefile.am.common' included from here
Makefile.am.common:14: warning: 'INCLUDES' is the old name for 'AM_CPPFLAGS' (or '*_CPPFLAGS')
include/libnet/Makefile.am:3:   'Makefile.am.common' included from here
Makefile.am.common:14: warning: 'INCLUDES' is the old name for 'AM_CPPFLAGS' (or '*_CPPFLAGS')
sample/Makefile.am:9:   'Makefile.am.common' included from here
Makefile.am.common:14: warning: 'INCLUDES' is the old name for 'AM_CPPFLAGS' (or '*_CPPFLAGS')
src/Makefile.am:9:   'Makefile.am.common' included from here
autoreconf: Leaving directory `.'

Just follow the advice and replace INCLUDES with AM_CPPFLAGS
Only distribute man pages for libnet headers. (Reported by g.esp)

Doxygen link files for directories were being packages up as man pages.