docs: ip-sysctl.txt: fix name of some ipv6 variables

The name of the following proc/sysctl entries were incorrectly
documented:

    /proc/sys/net/ipv6/conf/<interface>/max_dst_opts_number
    /proc/sys/net/ipv6/conf/<interface>/max_hbt_opts_number
    /proc/sys/net/ipv6/conf/<interface>/max_dst_opts_length
    /proc/sys/net/ipv6/conf/<interface>/max_hbt_length

Their name was set to the name of the symbol in the .data field of the
control table instead of their .proc name.
Signed-off-by: NOlivier Gayot <olivier.gayot@sigexec.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -1390,26 +1390,26 @@ mld_qrv - INTEGER
 	Default: 2 (as specified by RFC3810 9.1)
 	Minimum: 1 (as specified by RFC6636 4.5)
 
-max_dst_opts_cnt - INTEGER
+max_dst_opts_number - INTEGER
 	Maximum number of non-padding TLVs allowed in a Destination
 	options extension header. If this value is less than zero
 	then unknown options are disallowed and the number of known
 	TLVs allowed is the absolute value of this number.
 	Default: 8
 
-max_hbh_opts_cnt - INTEGER
+max_hbh_opts_number - INTEGER
 	Maximum number of non-padding TLVs allowed in a Hop-by-Hop
 	options extension header. If this value is less than zero
 	then unknown options are disallowed and the number of known
 	TLVs allowed is the absolute value of this number.
 	Default: 8
 
-max dst_opts_len - INTEGER
+max_dst_opts_length - INTEGER
 	Maximum length allowed for a Destination options extension
 	header.
 	Default: INT_MAX (unlimited)
 
-max hbh_opts_len - INTEGER
+max_hbh_length - INTEGER
 	Maximum length allowed for a Hop-by-Hop options extension
 	header.
 	Default: INT_MAX (unlimited)