tests: add a test for decoding and dumping of recvmmsg/sendmmsg

* configure (AC_CHECK_FUNCS): Add sendmmsg.
* tests/mmsg.c: New file.
* tests/mmsg.expected: New file.
* tests/mmsg.test: New test.
* tests/.gitignore: Add mmsg.
* tests/Makefile.am (CHECK_PROGRAMS): Add mmsg.
(TESTS): Add mmsg.test.
(EXTRA_DIST): Add mmsg.expected.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
diff --git a/configure.ac b/configure.ac
index 7862f65..f55af46 100644
--- a/configure.ac
+++ b/configure.ac
@@ -219,6 +219,7 @@
 	process_vm_readv
 	pwritev
 	sendmsg
+	sendmmsg
 	sigaction
 	stpcpy
 	strerror