genprotocol.pl: Fix code on FreeBSD too

genprotocol.pl: Fix code on FreeBSD too

On some systems (linux, cygwin and gnukfreebsd) rpcgen generates files
which when compiling produces this warning:

remote/remote_protocol.c: In function 'xdr_remote_node_get_cpu_stats_ret':
remote/remote_protocol.c:530: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]

Hence, on those systems we need to post-process the files by the
rpc/genprotocol.pl perl script. At the beginning of the script the OS is
detected via $^O perl variable. From my latest build on FreeBSD I see we
need to fix the code there too. On FreeBSD the variable contains
'freebsd' string:

http://perldoc.perl.org/perlport.html#PLATFORMS

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>