net: support 64bit values for setsockopt(SO_MAX_PACING_RATE)

64bit kernels now support 64bit pacing rates.

This commit changes setsockopt() to accept 64bit
values provided by applications.

Old applications providing 32bit value are still supported,
but limited to the old 34Gbit limitation.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>