conmon: update to 2.1.8

conmon: update to 2.1.8

Bug fixes:
 - stdio: ignore EIO for terminals
 - ensure console socket buffers are properly sized
 - conmon: drop return after pexit()
 - ctrl: make accept4 failures fatal
 - logging: avoid opening /dev/null for each write
 - oom: restore old OOM score
 - Use default umask 0022

Misc changes:
 - cli: log parsing errors to stderr
 - Changes to build conmon for riscv64
 - Changes to build conmon for ppc64le
 - Fix close_other_fds on FreeBSD

Signed-off-by: Oskari Rauta <oskari.rauta@gmail.com>