Use dlsym to load libstatssocket API

Also fixes a bug in the tests where the platform version was being
checked by querying version.release instead of version.codename
(currently, version.release == 10, while version.codename == R).

Test: bit libstatspush_compat_test:* (on Q and R)
Test: libsstatssocket.so is not placed in resolv apex (on R)

1|bonito:/ $ ls apex/com.android.resolv/lib64
libclang_rt.ubsan_standalone-aarch64-android.so
libcrypto.so
libnetd_resolv.so
libssl.so

Test: NETWORK_DNS_EVENT_REPORTED atom is logged to statsd (on R)
    - adb shell cmd stats print-stats (atom 116 count > 0)

Bug: 148743333
Change-Id: Ib3eaa32835905bcf6e3b003054bf0f3c4e7ec0a4