Move PRU_SOCKADDR request to (*pru_sockaddr)()

Move PRU_SOCKADDR request to (*pru_sockaddr)()

Introduce in{,6}_sockaddr() functions, and use them for all except tcp(4)
inet sockets. For tcp(4) sockets use tcp_sockaddr() to keep debug ability.

The key management and route domain sockets returns EINVAL error for
PRU_SOCKADDR request, so keep this behaviour for a while instead of make
pru_sockaddr handler optional and return EOPNOTSUPP.

ok bluhm@