ip: Use the `struct fib_rule_hdr` for rules

ip: Use the `struct fib_rule_hdr` for rules

The iprule.c code was using `struct rtmsg` as the data
type to pass into the kernel for the netlink message.
While 'struct rtmsg' and `struct fib_rule_hdr` are
the same size and mostly the same, we should use
the correct data structure.  This commit translates
the data structures to have iprule.c use the correct
one.

Additionally copy over the modified fib_rules.h file

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
Signed-off-by: David Ahern <dsahern@gmail.com>