SUNRPC: Don't allocate a full sockaddr_storage for tracing

We're always tracing IPv4 or IPv6 addresses, so we can save a lot
of space on the ringbuffer by allocating the correct sockaddr size.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: stable@vger.kernel.org
Fixes: 83a712e0

 "sunrpc: add some tracepoints around ..."
Signed-off-by: J. Bruce Fields <bfields@redhat.com>