netinfo: Never replace BOOTPROTO parameter from ifcfg

This is a backport of a (correct) behaviour in version 4.16,
as introduced in the commit 08c2cb4b085e70d21438a40d64cffe9625d20d22,
with Change-Id I88e8a4afa7759d37b9bd5c68a18d38baecfe94a6, reviewed
on http://gerrit.ovirt.org/28592

Change-Id: I44ab20769f85b19f7ab14d12428543cd5b62d60f
Bug-Url: https://bugzilla.redhat.com/1122475
Related-to: https://bugzilla.redhat.com/987813
Signed-off-by: Ondřej Svoboda <osvoboda@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/30646
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>