All tests pass with one exception: some Broxygen tests are broken
because dpd_config doesn't exist anymore. Need to update the mechanism
for auto-documenting well-known ports.
Added a generic gtpv1_message event generated for any GTP message type.
Added specific events for the create/update/delete PDP context
request/response messages.
Addresses #934.
This currently supports automatic decapsulation of GTP-U packets on
UDP port 2152.
The GTPv1 headers for such tunnels can be inspected by handling the
"gtpv1_g_pdu_packet" event, which has a parameter of type "gtpv1_hdr".
Analyzer and test cases are derived from submissions by Carsten Langer.
Addresses #690.