ifcfg-rh: use PKCS #12 private key also as client cert in reader

Before commit e3ac45c0 the reader set the private key in the
setting using the libnm function, which also set the key as client
certificate if it was in PKCS #12 format.

After the commit, existing connections with a PKCS #12 private key but
without a client certificate became invalid. Restore the old behavior.

Fixes: e3ac45c0 ('ifcfg-rh: don't use 802-1x certifcate setter functions')
12 jobs for bg/802-1x-client-cert-rh1705054 in 33 minutes and 59 seconds (queued for 42 seconds)
latest
Status Job ID Name Coverage
  Test
passed #305497
allowed to fail
checkpatch

00:01:01

passed #305504
t_debian:9

00:20:07

passed #305506
t_debian:sid

00:15:16

manual #305505
allowed to fail manual
t_debian:testing
passed #305498
t_fedora:28

00:23:19

passed #305499
t_fedora:29

00:33:26

passed #305500
t_fedora:30

00:31:45

manual #305501
allowed to fail manual
t_fedora:rawhide
passed #305502
t_ubuntu:16.04

00:13:46

passed #305503
t_ubuntu:18.04

00:15:33

 
  External
passed NetworkManager test verification

passed NetworkManager test verification

05:52:16