libnetapi: Fix style issues in previous commit.

libnetapi: Do not use the freebsd11_network headers globally.

Since they were being Use'd at global scope, the FreeBSD versions
of a number of POSIX headers were being used instead of the POSIX ones,
which breaks the build on non-x86 as these headers presently do not work
elsewhere.

Instead, just include the base directory, and then include the compat
headers manually in the one place that actually requires them.
Also fix all the other files that expected errno.h and others to
be included implicitly, which they now are not.

This should fix the PowerPC and (part of the) ARM builds.

libbnetapi: Extend socket classes.

B{Abstract,Datagram,Secure}Socket:
- Add functionality to listen for and accept new connections, thus allowing
one to use the socket classes for server functionality as well.

BSecureSocket:
- Adjust to take into account differences between how SSL needs to be called
when accepting an incoming connection vs initiating an outbound one.
The handshake on the accepted connection stills fails for unknown reasons
at the moment though.

Note that these changes break the ABI, and thus any packages making use of
them directly will need a rebuild.

Revert "Move getifaddrs to libnetwork again."

This reverts commit 31ea76548a64b232ed10cb444bf84ca1f7e40b0f.

Adrien, please try again without clobbering the otherwise nice
BNetworkInterface API!

Conflicts:
src/kits/network/getifaddrs.cpp

Move getifaddrs to libnetwork again.

* BNetworkInterfaceAddress is moved to libnetwork. It is modified to not
use BNetworkAddress (which is in libbnetapi) and instead use sockaddr
and sockaddr_storage directly. All callers are adjusted to this.
* Some support code is shared between BNetworkInterface and
BNetworkInterfaceAddress, move it to libnetwork but in the BPrivate
namespace.

Use ssize_t to allow returning a negative error code

Added experimental version of a Socket API with SSL support.

* Each class has a Socket() method to retrieve the underlaying file descriptor
to be able to do the more advanced stuff, if necessary.
* A server socket is yet missing, but the rest is pretty much covered.

Revert "Move getifaddrs to libnetwork again."

This reverts commit 31ea76548a64b232ed10cb444bf84ca1f7e40b0f.

Adrien, please try again without clobbering the otherwise nice
BNetworkInterface API!

Conflicts:
src/kits/network/getifaddrs.cpp

Move getifaddrs to libnetwork again.

* BNetworkInterfaceAddress is moved to libnetwork. It is modified to not
use BNetworkAddress (which is in libbnetapi) and instead use sockaddr
and sockaddr_storage directly. All callers are adjusted to this.
* Some support code is shared between BNetworkInterface and
BNetworkInterfaceAddress, move it to libnetwork but in the BPrivate
namespace.

Use ssize_t to allow returning a negative error code

Added experimental version of a Socket API with SSL support.

* Each class has a Socket() method to retrieve the underlaying file descriptor
to be able to do the more advanced stuff, if necessary.
* A server socket is yet missing, but the rest is pretty much covered.