libpdx_uds: Fix send/receive over socket to handle signal interrupts

Previous implementation of send/receive didn't account for the fact that
send/receive operation might be interrupted by a signal and transfer
fewer bytes than requested.

Fix this by repeatedly calling send/recv until all the requested data
is transferred over sockets.

Also added a number of unit tests for send/receive functions.

Bug: 37427314
Test: `m -j32` succeeds for Sailfish.
      `libpdx_uds_tests` pass on device

Change-Id: Ib8f78967af3c218d9f18fb3dfe8953c35800540b