DAHDI trunkdev support

DAHDI trunkdev is a newly-introduced 'virtual trunk' character device
which is used instead of a real hardware driver. This means that an
application (such as osmo-e1d) can implement a virtual E1 trunk and
receive and transmit E1 frame data which is exposed to DAHDI users
just like the data from a real physical E1 span.

In order to build DAHDI trunkdev support into osmo-e1d, you will need
a special fork of dahdi containing the required support, currently
the laforge/trunkdev branch of the following repository:
	https://gitea.osmocom.org/retronetworking/dahdi-linux

Change-Id: Ib15a7313fcd63e1ed9f2f5b349df967bc4335ec2
---
M configure.ac
M include/osmocom/octoi/octoi.h
M src/Makefile.am
A src/dahdi_trunkdev.c
M src/e1d.h
M src/e1oip.c
M src/intf_line.c
M src/log.c
M src/log.h
M src/octoi/octoi.c
M src/octoi/octoi_clnt_vty.c
M src/octoi/octoi_srv_fsm.c
M src/octoi/octoi_srv_vty.c
M src/octoi/octoi_vty.h
M src/vty.c
15 files changed, 490 insertions(+), 15 deletions(-)