src: initial extended netlink error reporting

This patch correlates the in-kernel extended netlink error offset and
the location information.

Assuming 'foo' table does not exist, then error reporting shows:

 # nft delete table foo
 Error: Could not process rule: No such file or directory
 delete table foo
              ^^^

Similarly, if table uniquely identified by handle '1234' does not exist,
then error reporting shows:

 # nft delete table handle 1234
 Error: Could not process rule: No such file or directory
 delete table handle 1234
                     ^^^^

 Assuming 'bar' chain does not exists in the kernel, while 'foo' does:

 # nft delete chain foo bar
 Error: Could not process rule: No such file or directory
 delete chain foo bar
                  ^^^

 This also gives us a hint when adding rules:

 # nft add rule ip foo bar counter
 Error: Could not process rule: No such file or directory
 add rule ip foo bar counter
             ^^^

This is based on ("src: basic support for extended netlink errors") from
Florian Westphal, posted in 2018, with no netlink offset correlation
support.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 740c21f2..9142ab44 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -32,6 +32,7 @@ libnftables_la_SOURCES =			\
 		rule.c				\
 		statement.c			\
 		cache.c				\
+		cmd.c				\
 		datatype.c			\
 		expression.c			\
 		evaluate.c			\