libvpd: Fix compilation issue
libvpd: Fix compilation issue

compilation error:
/bin/sh ./libtool  --tag=CXX   --mode=compile g++ -DHAVE_CONFIG_H -I. -I./src/libvpd-2 -I./src/   -DDEST_DIR='"/usr/local"' -g -O2 -MT helper_functions.lo -MD -MP -MF .deps/helper_functions.Tpo -c -o helper_functions.lo `test -f 'src/helper_functions.cpp' || echo './'`src/helper_functions.cpp
libtool: compile:  g++ -DHAVE_CONFIG_H -I. -I./src/libvpd-2 -I./src/ -DDEST_DIR=\"/usr/local\" -g -O2 -MT helper_functions.lo -MD -MP -MF .deps/helper_functions.Tpo -c src/helper_functions.cpp  -fPIC -DPIC -o .libs/helper_functions.o
src/helper_functions.cpp: In static member function 'static std::string lsvpd::HelperFunctions::findAIXFSEntry(std::vector<lsvpd::DataItem*>, const string&)':
src/helper_functions.cpp:57:13: error: 'close' was not declared in this scope
     close(fd);
                  ^
src/helper_functions.cpp: In static member function 'static std::string lsvpd::HelperFunctions::getSymLinkTarget(const string&)':
src/helper_functions.cpp:162:15: error: 'readlink' was not declared in this scope
linkTarget));
^
make: *** [helper_functions.lo] Error 1

This patch fixes above compilation issue by adding unistd.h header file.

Signed-off-by: Vasant Hegde <a6d753843573f7bfed5075c1e875b0be8007a0ab@linux.vnet.ibm.com>
Acked-by: Suzuki K Poulose <2d5cd350c7a48263c670a6374c5c55bca8d1a68a@in.ibm.com>

kamalesh-babulal/libvpd,jananive/libvpd,jananive/libvpd,kamalesh-babulal/libvpd,jananive/libvpd,kamalesh-babulal/libvpd