core: add PPP support

This patch add PPP support. NS3 and real PPP traces are supported now
and the ppp dpkt disector is now enabled. Fixes #8

Reported-by: Clemens John <clemens-john@gmx.de>
Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>

captcp.py

@@ -521,6 +521,8 @@ def __init__(self, pcap_file_path, pcap_filter):
                 dpkt.pcap.DLT_LOOP:      dpkt.loopback.Loopback,
                 dpkt.pcap.DLT_NULL:      dpkt.loopback.Loopback,
                 dpkt.pcap.DLT_EN10MB:    dpkt.ethernet.Ethernet,
+                dpkt.pcap.DLT_IEEE802:   dpkt.ethernet.Ethernet,
+                dpkt.pcap.DLT_PPP:       dpkt.ppp.PPP,
                 dpkt.pcap.DLT_LINUX_SLL: dpkt.sll.SLL
             }[self.pc.datalink()]
         except KeyError: