selftests/net: add definition for SOL_DCCP to fix compilation errors for old libc

Many systems build/test up-to-date kernels with older libcs, and
an older glibc (2.17) lacks the definition of SOL_DCCP in
/usr/include/bits/socket.h (it was added in the 4.6 timeframe).

Adding the definition to the test program avoids a compilation
failure that gets in the way of building tools/testing/selftests/net.
The test itself will work once the definition is added; either
skipping due to DCCP not being configured in the kernel under test
or passing, so there are no other more up-to-date glibc dependencies
here it seems beyond that missing definition.

Fixes: 11fb60d1089f ("selftests: net: reuseport_addr_any: add DCCP")
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: net: reuseport_addr_any: silence clang warning

Clang does not recognize that calls to error() terminate execution
and complains about uninitialized variable use that happens after calls
to error(). This noop patchset fixes this.

Signed-off-by: Peter Oskolkov <posk@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: net: refactor reuseport_addr_any test

This patch refactors reuseport_add_any selftest a bit:
- makes it more modular (eliminates several copy/pasted blocks);
- skips DCCP tests if DCCP is not supported

V2: added "Signed-off-by" tag.

Signed-off-by: Peter Oskolkov <posk@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: net: reuseport_addr_any: add DCCP

This patch adds coverage of DCCP to reuseport_addr_any selftest.

Signed-off-by: Peter Oskolkov <posk@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: net: test that listening sockets match on address properly

This patch adds a selftest that verifies that a socket listening
on a specific address is chosen in preference over sockets
that listen on any address. The test covers UDP/UDP6/TCP/TCP6.

It is based on, and similar to, reuseport_dualstack.c selftest.

Signed-off-by: Peter Oskolkov <posk@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>