SocketClient: don't ignore SIGPIPE

1) All current users are better off ignoring SIGPIPE at the beginning
   of their process instead of ignoring it just for SocketClient
2) This isn't thread safe if users did want it, since sigaction()
   ignores SIGPIPE for the entire process
3) This costs 5-10% of logd CPU time when logcat is reading logs

Also clean up the error handling in SocketClient::sendDataLockedv().

Test: kill logcat and see that logd doesn't crash
Test: run simpleperf and see that no cycles are going to sigaction
Change-Id: I6532c8a0d71338e534411707b9a9bd785145c730