fp6-device-tweaks 6: run ModemManager in its quick suspend/resume mode

Deep suspend on the FP6 is ended every few seconds by the modem's QMI
indications that ModemManager subscribes to: signal info on a 5 dB delta,
system info, DSD system status (16 + 3 of 25 deep cycles on 2026-10-14).
ModemManager already has the answer: started with
--test-quick-suspend-resume it sets the modem "terse" on logind's
PrepareForSleep (those subscriptions off, calls and texts still delivered)
and synchronises on resume. On the dev phone a logind-driven deep cycle
then runs to its 60 s alarm with the modem registered and imsd up, where
none of 21 did before.

Ship the flag as a drop-in. It does nothing while the sleep targets stay
masked, and is the modem side of the suspend policy when they go.

aports/device/fp6-device-tweaks/modemmanager-quick-suspend.conf

@@ -0,0 +1,11 @@
+# ModemManager's quick suspend/resume mode (fp6 repo journal/power/, 2026-10-14):
+# on logind's PrepareForSleep the modem is set "terse" (the NAS signal-info,
+# system-info and DSD system-status subscriptions are dropped, calls and
+# texts still reach us) and on resume its state is synchronised. Without it
+# the modem's indications end a deep suspend cycle every few seconds; with
+# it a cycle runs to its wake alarm while the modem stays registered. The
+# option still carries MM's --test- prefix; it is the only switch for the
+# daemon's built-in terse mode.
+[Service]
+ExecStart=
+ExecStart=/usr/sbin/ModemManager --test-quick-suspend-resume