Get the original xprobe2-0.3 from Sourceforge:

http://downloads.sourceforge.net/project/xprobe/xprobe2/Xprobe2%200.3/xprobe2-0.3.tar.gz

Uncompress it under, for example /tmp/xprobe2-0.3 directory

Copy the diff file at /tmp

Execute the patch command:

 patch -p1 < ../xprobe2-0.3.diff.patch 

This should look like:

patching file CHANGELOG
patching file config.status
patching file configure
patching file libs-external/USI++/src/config.h
patching file libs-external/USI++/src/config.log
patching file libs-external/USI++/src/config.status
patching file libs-external/USI++/src/ip.cc
patching file libs-external/USI++/src/Makefile
patching file libs-external/USI++/src/misc.cc
patching file libs-external/USI++/src/usi++/arp.h
patching file libs-external/USI++/src/usi++/config.h
patching file libs-external/USI++/src/usi++/datalink.h
patching file libs-external/USI++/src/usi++/icmp.h
patching file libs-external/USI++/src/usi++/if.h
patching file libs-external/USI++/src/usi++/ip.h
patching file libs-external/USI++/src/usi++/Layer2.h
patching file libs-external/USI++/src/usi++/README
patching file libs-external/USI++/src/usi++/RX.h
patching file libs-external/USI++/src/usi++/tcp.h
patching file libs-external/USI++/src/usi++/TX.h
patching file libs-external/USI++/src/usi++/TX_IP.h
patching file libs-external/USI++/src/usi++/udp.h
patching file libs-external/USI++/src/usi++/usi++
patching file libs-external/USI++/src/usi++/usi++.h
patching file libs-external/USI++/src/usi++/usi-structs.h
patching file libs-external/USI++/usi++/config.h
patching file libs-external/USI++/usi++/tcp.h
patching file Makefile
patching file src/config.h
patching file src/defines.h
patching file src/Makefile
patching file src/xplib/Makefile
patching file src/xpmodules/alive_probe/Makefile
patching file src/xpmodules/alive_probe/portscanner/Makefile
patching file src/xpmodules/alive_probe/ttl_calc/Makefile
patching file src/xpmodules/Makefile
patching file src/xpmodules/os_probe/icmp_addrmask/Makefile
patching file src/xpmodules/os_probe/icmp_echo_id/Makefile
patching file src/xpmodules/os_probe/icmp_inforeq/Makefile
patching file src/xpmodules/os_probe/icmp_port_unreach/Makefile
patching file src/xpmodules/os_probe/icmp_timestamp/Makefile
patching file src/xpmodules/os_probe/Makefile
patching file src/xpmodules/os_probe/smb/Makefile
patching file src/xpmodules/os_probe/snmp/Makefile
patching file src/xpmodules/os_probe/tcp_handshake/Makefile
patching file src/xpmodules/os_probe/tcp_rst/Makefile

Your patched code is now ready to be used.