wwan/modem-broadband: look up default APN if GSM conneciton lacks one

This allows the GSM connection to Just Work most of the time, as in:
"nmcli d connect ttyUSB0".
13 jobs for lr/gsm-default-apn in 38 minutes and 35 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #381037
allowed to fail
checkpatch

00:01:04

manual #381042
allowed to fail manual
t_centos:7.5.1804
failed #381043
t_centos:7.6.1810

00:15:32

failed #381046
t_debian:9

00:09:25

failed #381048
t_debian:sid

00:09:26

manual #381047
allowed to fail manual
t_debian:testing
passed #381038
t_fedora:28

00:29:30

passed #381039
t_fedora:29

00:37:35

passed #381040
t_fedora:30

00:33:42

manual #381041
allowed to fail manual
t_fedora:rawhide
failed #381044
t_ubuntu:16.04

00:09:52

failed #381045
t_ubuntu:18.04

00:09:58

 
  External
canceled NetworkManager test verification

00:25:14

 
Name Stage Failure
failed
t_centos:7.6.1810 Test
+ find -name '*.valgrind-log' -print0
>>>> PRINT VALGRIND LOGS (valgrind test) (done)
valgrind test failed
+ true
+ echo '>>>> PRINT VALGRIND LOGS (valgrind test) (done)'
+ die 'valgrind test failed'
+ printf '%s\n' 'valgrind test failed'
+ exit 1
ERROR: Job failed: exit code 1
failed
t_ubuntu:18.04 Test
Has header "pppd/pppd.h" : YES 
Program pppd found: YES (/usr/sbin/pppd)
Run-time dependency mm-glib found: YES 1.10.0
Run-time dependency mobile-broadband-provider-info found: NO (tried pkgconfig)

meson.build:502:2: ERROR: Dependency "mobile-broadband-provider-info" not found, tried pkgconfig

A full log can be found at /builds/NetworkManager/NetworkManager/build/meson-logs/meson-log.txt
ERROR: Job failed: exit code 1
failed
t_ubuntu:16.04 Test
Has header "pppd/pppd.h" : YES 
Program pppd found: YES (/usr/sbin/pppd)
Run-time dependency mm-glib found: YES 1.6.4
Run-time dependency mobile-broadband-provider-info found: NO (tried pkgconfig)

meson.build:502:2: ERROR: Dependency "mobile-broadband-provider-info" not found, tried pkgconfig

A full log can be found at /builds/NetworkManager/NetworkManager/build/meson-logs/meson-log.txt
ERROR: Job failed: exit code 1
failed
t_debian:sid Test
Has header "pppd/pppd.h" : YES
Program pppd found: YES (/usr/sbin/pppd)
Dependency mm-glib found: YES 1.10.0
Dependency mobile-broadband-provider-info found: NO (tried pkgconfig)

meson.build:502:2: ERROR: Dependency "mobile-broadband-provider-info" not found, tried pkgconfig

A full log can be found at /builds/NetworkManager/NetworkManager/build/meson-logs/meson-log.txt
ERROR: Job failed: exit code 1
failed
t_debian:9 Test
Has header "pppd/pppd.h" : YES 
Program pppd found: YES (/usr/sbin/pppd)
Run-time dependency mm-glib found: YES 1.6.4
Run-time dependency mobile-broadband-provider-info found: NO (tried pkgconfig)

meson.build:502:2: ERROR: Dependency "mobile-broadband-provider-info" not found, tried pkgconfig

A full log can be found at /builds/NetworkManager/NetworkManager/build/meson-logs/meson-log.txt
ERROR: Job failed: exit code 1