package/grpc: bump version to 1.30.2

Other changes:
  - Add a dependency on libabseil-cpp
  - Update the patches to apply properly.

Tested with the following distributions:
  - Debian 9
  - CentOS 7
  - Fedora 32

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>