rconn: Maintain original allowed_versions instead of substituting for zero.

rconn: Maintain original allowed_versions instead of substituting for zero.

rconn_create() was substituting OFPUTIL_DEFAULT_VERSIONS if an
allowed_versions of 0 was passed in.  At the same time,
connmgr_set_controllers() compared the adjusted value of allowed_versions
against the original value, saw that they were different, and concluded
that it should kill off and recreate the rconn with the "corrected"
allowed_versions.

This commit fixes the problem by no longer adjusting allowed_versions.
There is no need, because it is only used in contexts where the original
version is OK.

This problem was introduced by commit 90ef0206ea8f5a39 (connmgr:
Reinitialise controllers if protocols changes).

Bug #14126.
CC: Simon Horman <horms@verge.net.au>
Reported-by: Natasha Gude <natasha@nicira.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>