pass socket address in our or out. This makes Linux programs using IPv6
working under emulation. This addresses kern/13279 by Jun-ichiro itojun Hagino.
Change sendmsg()/recvmsg() to expect the control information
to be passed the standard way (not 4.3BSD one, imlied by compat_43 code
or MSG_COMPAT). Linux uses different (arguably broken) CMSG_ALIGN() on some
architectures unfortunately, that would need to be handled eventually.
Also provide some other trivial stubs (like linux_sys_send()) to avoid
unneeded dependance on uipc_syscalls_43.c.
jdolecek