Unlock sysctl net.inet.ip.redirect and net.inet6.ip6.redirect.

Unlock sysctl net.inet.ip.redirect and net.inet6.ip6.redirect.

Variable ip and ip6 sendredirects is only read once during packet
processing.  Use atomic_load_int() to access the value in exactly
one read instruction.  No memory barriers needed as there is no
correlation with other values.
Sort the ip and ip6 checks, so the difference is easier to see.
Move access to global variable to the end.

OK mvs@