ifcfg-rh: refactor parsing bond options

Don't use g_strsplit_set() if all we want to do is split the
string at the first '='.
6 jobs for <span class="ref-name">th/strsplit-pt2</span> in 26 minutes and 45 seconds (queued for 50 seconds)
Status Job ID Name Coverage
  Test
passed #233069
build_f28

00:25:30

passed #233070
build_f29

00:22:58

passed #233071
build_f30

00:24:56

failed #233072
allowed to fail
build_frawhide

00:16:30

passed #233068
allowed to fail
checkpatch

00:01:57

 
  External
canceled NetworkManager test verification

03:52:10

 
Name Stage Failure
failed
build_frawhide Test
UUID=a66f2806-73d3-4fa5-a56e-b80a8a5226f0
BASEDIR=/builds/NetworkManager/NetworkManager/contrib/fedora/rpm/NetworkManager.20190412-085833.Q6e8wM
warning: Macro expanded in comment on line 144: %{real_version_major}/%{name}-%{real_version}.tar.xz

error: This macro requires some arguments
error: line 858: %systemd_postun

ERROR: rpmbuild FAILED
ERROR: Job failed: exit code 1