Install libpcap on your system. Should your version be different from the one used for the .so here just try to symlink to the version requested, the features we use should be available in most versions.
cp jpcap/0.7/jpcap.jar /usr/lib/flume/lib/
cp jpcap/0.7/libjpcap.so-i386 /usr/lib/flume/lib/libjpcap.so # Choose your architecture (i386 or x86_64)
cp target/flume-plugin-pcap-0.0.1-SNAPSHOT.jar /usr/lib/flume/lib/
Set the following properties in your configuration (flume-site.xml):
flume.plugin.classes = com.cloudera.flume.handlers.PcapSource
flume.plugin.outputformat.classes = com.cloudera.flume.handlers.PcapOutputFormat