libsearpc: Update to "new" version, switch to git download method

libsearpc: Update to "new" version, switch to git download method

Upstream changed the v3.2.0 tag. Previously it referred to
haiwen/libsearpc@23f581b39fa4555ede80efe2729f76e6159e8b7a; now it refers
to haiwen/libsearpc@d1fd7518a20b25766ff98d6fde6e40c63626ca0d.

This changes the packaged version to the "new" v3.2.0 and switches to
using the git download method (technically the github_archive method),
since the codeload filenames of the previous and current versions are
the same but the files have different hashes.

Signed-off-by: Jeffery To <redacted>