ovn-sb.xml: Correct statement on use of bit ranges.
Bit range specifiers can be used only with ordinal fields.
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- Any use of a nominal field may specify a single bit or a range of
+ Any use of a ordinal field may specify a single bit or a range of
bits, e.g. <code>vlan.tci[13..15]</code> refers to the PCP field
within the VLAN TCI, and <code>eth.dst[40]</code> refers to the
multicast bit in the Ethernet destination address.
