Add direct report back when registerForNtnSignalStrength is invoked

There is a case that caller has requested to report ntn signal strength, but no report for a whille as there is not signal strength happens.
Therefore added a immediate report back when registerForNtnSignalStrength is invoked

Bug: 353593633
Flag: EXEMPT bugfix
Test: atest SatelliteControllerTest
    manually e2e test and check whether direct reports triggered by log checking
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:74abda9fa04488044d7897ee062822656b3c09f6)
Merged-In: I17bd7f7989171ec64a6b38a73665552a2619080a
Change-Id: I17bd7f7989171ec64a6b38a73665552a2619080a