contrib: add a Bluetooth DUN modem emulator

Useful for quickly testing Bluetooth DUN support. Duplicates some
modemu.pl logic, but hey...
18 jobs for lr/btmodem.pl in 105 minutes and 5 seconds (queued for 23 seconds)
latest
Status Job ID Name Coverage
  Test
passed #678945
allowed to fail
checkpatch

00:01:08

manual #678951
allowed to fail manual
t_centos:7.5.1804
passed #678952
t_centos:7.6.1810

00:26:08

passed #678958
t_debian:10

00:22:40

passed #678957
t_debian:9

00:22:25

passed #678960
t_debian:sid

00:20:58

manual #678959
allowed to fail manual
t_debian:testing
manual #678946
allowed to fail manual
t_fedora:28
passed #678947
t_fedora:29

00:35:48

passed #678948
t_fedora:30

00:32:15

passed #678949
t_fedora:31

00:28:24

manual #678950
allowed to fail manual
t_fedora:rawhide
passed #678953
t_ubuntu:16.04

00:20:29

passed #678954
t_ubuntu:18.04

00:23:43

manual #678956
allowed to fail manual
t_ubuntu:devel
manual #678955
allowed to fail manual
t_ubuntu:rolling
 
  External
failed https://desktopqe-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/beaker-NetworkManager-gitlab-trigger-code-upstream/765/

failed https://desktopqe-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/beaker-NetworkManager-gitlab-trigger-code-upstream/765/

05:49:50