curvetun: renamed client, server, and management files

Rename those files so that they are conform to the rest of the files
we have in our repository.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
curvetun_client: include crypto instead of single nacl header

Use the common crypto header file as this is intended for that.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
curvetun_mgmt: consolidate the two mgmt include files into one

Consolidate the two mgmt include files into one.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>