local header files available in the project but make gives No such file or directory error

From entire day I am trying to install OverSim [http://www.oversim.org/wiki/OverSimInstall] The make file looks like this:

all: checkmakefiles
    cd src && $(MAKE)

clean: checkmakefiles
    cd src && $(MAKE) clean

cleanall: checkmakefiles
    cd src && $(MAKE) MODE=release clean
    cd src && $(MAKE) MODE=debug clean
    rm -f src/Makefile

makefiles:
    cd src && opp_makemake -f --deep --make-so -o inet -O out $$NSC_VERSION_DEF

checkmakefiles:
    @if [ ! -f src/Makefile ]; then \
    echo; \
    echo '======================================================================='; \
    echo 'src/Makefile does not exist. Please use "make makefiles" to generate it!'; \
    echo '======================================================================='; \
    echo; \
    exit 1; \
    fi

doxy:
    doxygen doxy.cfg

tcptut:
    cd doc/src/tcp && $(MAKE)

I am using Omnet5.1.1 as omnet4.2.2 is not supported on Ubuntu16.04, my gcc version is 5.4.1.

Every time I try to build this make all, it gives header file not found error where as in actual the header files are present inside the project directory.

In file included from applications/ethernet/EtherAppCli.cc:21:0:
applications/ethernet/EtherAppCli.h:21:22: fatal error: INETDefs.h: No such file or directory

The includes are done like this:

#include "INETDefs.h" //available at src/linklayer/contract/
#include "MACAddress.h" //available at src/base/

project structure:

How could I resolve this build error?