net: struct sockaddr should have field "sa_family"

POSIX requires struct sockaddr's field to be named "sa_family"
(not just "family"):
http://pubs.opengroup.org/onlinepubs/009696699/basedefs/sys/socket.h.html



This change allows to port POSIX apps easier (including writing
portable apps using BSD Sockets compatible API).

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>