OCTOI: initial support for E1oIP forwarding

This introduces initial support for operation as OCTOI (Osmocom
Community TDMoIP) server and client operation.

Various features are still absent (user authentication, support for
re-ordered packets), but this version is already able to provide
services to clients with dynamic IP addresses as well as servers.

The bulk of the OCTOI / E1oIP code is implemented as a shared library,
to facilitate the development of other servers and clients in the
future, and also to minimize the impact on the existing osmo-e1d code
base.

More information is available at https://osmocom.org/projects/octoi/wiki

Change-Id: I05f5ff697ca8f7dccdcf89660f12089babfcc92e
---
M configure.ac
M include/Makefile.am
M include/osmocom/e1d/proto.h
A include/osmocom/octoi/e1oip_proto.h
A include/osmocom/octoi/octoi.h
M src/Makefile.am
M src/ctl.c
M src/e1d.h
A src/e1oip.c
M src/intf_line.c
M src/mux_demux.c
A src/octoi/Makefile.am
A src/octoi/e1oip.c
A src/octoi/e1oip.h
A src/octoi/frame_fifo.c
A src/octoi/frame_fifo.h
A src/octoi/libosmo-octoi.map
A src/octoi/octoi.c
A src/octoi/octoi.h
A src/octoi/octoi_clnt_fsm.c
A src/octoi/octoi_clnt_vty.c
A src/octoi/octoi_fsm.c
A src/octoi/octoi_fsm.h
A src/octoi/octoi_sock.c
A src/octoi/octoi_sock.h
A src/octoi/octoi_srv_fsm.c
A src/octoi/octoi_srv_vty.c
A src/octoi/octoi_vty.h
M src/osmo-e1d.c
M src/usb.c
M src/vty.c
31 files changed, 3,387 insertions(+), 11 deletions(-)