devel/libsearpc: update 3.0.7 -> 3.1.0

• Fix memory leak
• allow return NULL for json return type
• Support json param type.
• Support json value in async mode.
• Add license file

PR: 214658
Changes: https://github.com/haiwen/libsearpc/commits/v3.1-latest
Submitted by: Ultima1252@gmail.com (maintainer)