Update tests to reflect the new HTTP dissector.
Update to reflect that BGP no longer prints a redundant length value.
Don't subtract the UDP header size from the length twice.
Fix length fields in UDP headers to be what they should be.

The value of the length field in a UDP header includes the length of the
header itself; the values in this capture didn't.  The length fields in
the IP headers and the RADIUS headers were correct and consistent with
each other, and the length fields in the UDP headers are now correct and
consistent with both of them.
Do bounds checking when unescaping PPP.

Clean up a const issue while we're at it.
Strengthen various bounds etc. checks.

Add more checks, make some checks do a better job of handling too-short
lengths,

Also, rename ldp_msg_print() to ldp_pdu_print(), as it prints a single
PDU, not a single message within a PDU.
Don't run past the snapshot length when doing hex/ASCII dumps.
Use system libpcap when configured with --with-system-pcap

Don't force the local libpcap build when the system provides one. When
--with-system-pcap is given to configure, don't try to locate a local libpcap
build. This help build systems like Buildroot that store build trees in the
same directory, but still prefer dynamically linking against system wide
libpcap.so to save space.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Merge pull request #408 from baruchsiach/system-libpcap

Use system libpcap when configured with --with-system-pcap