[PATCH nft] Improve handling of errors from mnl* functions"

[Eugene Crosser <crosser@average.org>]

Libnftables does not handle errors that libmnl functions may return
properly:

1. Retriable errors indicated by errno=EINTR are not retried, but
   rather treted as fatal.
2. Instead of reporting the error to the caller, functions call
   exit() on error, which terminates the caller process.

This patch set partly addresses the second point, by calling
abort() instead of exit() on ABI error, that will at least give
more information to the sysadmin than quiet termination of a
process.

It attempts to properly address the first point, by introducing
retry logic when mnl_socket_recvfrom() or mnl_cb_run() return
-1 with errno=EINTR.

It would be desirable to fully address the second point at some
future time, though it requires some redesign of the code structure.

 [PATCH nft 1/2] Use abort() in case of netlink_abi_error
 [PATCH nft 2/2] Handle retriable errors from mnl functions