sysctl man page update for pattern

sysctl  man page update for pattern

pattern must be used before `--system` else it does not work for sysctl
file(s)

```
root# /sbin/sysctl --system --pattern '^net.ipv6'
* Applying /etc/sysctl.d/30-ceph-osd.conf ...
fs.aio-max-nr = 1048576
kernel.pid_max = 4194304
* Applying /etc/sysctl.d/protect-links.conf ...
fs.protected_hardlinks = 1
fs.protected_symlinks = 1
* Applying /etc/sysctl.d/sara_tweaks.conf ...
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 0
* Applying /etc/sysctl.conf ...
```

vs:
```
root# /sbin/sysctl --pattern '^net.ipv6' --system
* Applying /etc/sysctl.d/30-ceph-osd.conf ...
* Applying /etc/sysctl.d/protect-links.conf ...
* Applying /etc/sysctl.d/sara_tweaks.conf ...
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 0
* Applying /etc/sysctl.conf ...
```

References:
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