selinux: don't log SELINUX_INFO and SELINUX_WARNING messages to audit

selinux: don't log SELINUX_INFO and SELINUX_WARNING messages to audit

Previously we logged even info message from libselinux as USER_AVC's to
audit. For example, setting SELinux to permissive mode generated
following audit message,

time->Tue Feb 26 11:29:29 2019
type=USER_AVC msg=audit(1551198569.423:334): pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='avc:  received setenforce notice (enforcing=0)  exe="/usr/lib/systemd/systemd" sauid=0 hostname=? addr=? terminal=?'

This is unnecessary and wrong at the same time. First, kernel already
records audit event that SELinux was switched to permissive mode, also
the type of the message really shouldn't be USER_AVC.

Let's ignore SELINUX_WARNING and SELINUX_INFO and forward to audit only
USER_AVC's and errors as these two libselinux message types have clear
mapping to audit message types.