Xdp-tools modifications

Modifications made to the xdp-tools repo in order to get everything to build and install properly

Be warned that changes in this code are often checked in which break the build (due to, Ahem!, things like putting headers in different directories and not changing the makefile, Ahem!).

modified configure file to change include directory

from
     LIBBPF_INCLUDE_DIR='$(LIB_DIR)/libbpf/src/root/usr/include'
to 
     LIBBPF_INCLUDE_DIR='$(LIB_DIR)/libbpf/src/root/include'

modified lib/Makefile to enable installation of libbpf (get all indents right!)

all: $(SUBDIRS) libxdp   ------>  all: $(SUBDIRS) libxdp libbpf
 
install: libxdp_install  ------>  install: libxdp_install libbpf_install

libbpf: $(OBJECT_LIBBPF) ------>

.PHONY: libbpf_install
libbpf_install: libbpf
       install -m 0755 -d $(DESTDIR)$(HDRDIR)
       $(MAKE) -C libbpf/src install

.PHONY: libbpf
 libbpf: $(OBJECT_LIBBPF)
       @echo; echo "  $@"; $(MAKE) -C $@/src

modified lib/libxdp/Makefile by adding these lines to the "install" target to enable installation of header files

$(Q)install -d -m 0755 $(DESTDIR)$(HDRDIR)/xdp
$(Q)install -m 0644 $(LIB_HEADERS) $(DESTDIR)$(HDRDIR)/xdp