When supported by the D-Bus daemon, it's better to have service files
in /usr rather than in /etc. Change the path for RHEL 8.

See also commit ef8c29288149 ('contrib/rpm: install D-Bus service
files to /usr if we can').

Service files shipped by distribution should be in /usr.

Some fixes for creating wpa_supplicant config.

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/826

wpa-eap-suite-b-192 key-mgmt method uses special values for "pairwise"
and "group" ciphers, we can also handle that a few lines underneath
where those are set to make this a bit easier to read.

We currently set the supplicants PMF config (ieee80211w) inside an if
block that tries to detect whether WPA is used. That if-block doesn't
include the "wpa-eap-suite-b-192" case because we want special
"pairwise" and "group" handling for wpa-eap-suite-b-192. This means
we're currently missing to enable PMF in the "wpa-eap-suite-b-192" case,
even though it's set to REQUIRED.

Fix it by moving the "pairwise" and "group" special-casing down a bit so
we can include "wpa-eap-suite-b-192" in the "Only WPA-specific things
when using WPA" check, that will make sure ieee80211w gets set in the
wpa-eap-suite-b-192 case.

A small bug sneaked into commit 3ef3733c8139 ('wireless-security: ensure
Mesh networks can't use anything but SAE') during review: Instead of
allowing only "sae" or "none" as key-mgmt, we now disallow "sae" and
"none", but allow anything else. This is obviously not what was
intended, so fix the check.

Also move the valid_key_mgmt check back up to where it was before that
commit, it seems we want to apply that check in all cases.

wpa-eap-suite-b-192 is also valid here, so mention it in the error
message.

We only set the "ieee80211w" option in the wpa_supplicant config in case
we're using WPA (see the if-block underneath), otherwise the value of
"pmf" is completely ignored. That means the override here (in case WPA
isn't used) isn't getting applied anyway, so just remove it.

It looks a bit weird on the first glance that we do nothing when
NM_SETTING_WIRELESS_SECURITY_PMF_OPTIONAL is used. The reason for this
is that we already intialize the global option "pmf" of wpa_supplicant
to "1" (optional), so add a brief comment about that here.