tools: Fix `frr-reload.py` error related to `static-sids`

tools: Fix `frr-reload.py` error related to `static-sids`

```
[...]
segment-routing
 srv6
  static-sids
   sid fcbb:bbbb:1::/48 locator MAIN behavior uN
   sid fcbb:bbbb:1:fe10::/64 locator MAIN behavior uDT4 vrf Vrf10
   sid fcbb:bbbb:1:fe20::/64 locator MAIN behavior uDT6 vrf Vrf20
   sid fcbb:bbbb:1:fe30::/64 locator MAIN behavior uDT46 vrf Vrf30
   sid fcbb:bbbb:1:fe40::/64 locator MAIN behavior uA interface sr0 nexthop 2001::2
[...]
```

When the user has a configuration like the one above and runs the
command `frr-reload.py --reload`, the following error occurs:

```
[1129654|mgmtd] sending configuration
line 17: % Unknown command[76]:   sid fcbb:bbbb:1::/48 locator MAIN behavior uN
line 23: % Unknown command[76]:   sid fcbb:bbbb:1:fe10::/64 locator MAIN behavior uDT4 vrf Vrf10
line 29: % Unknown command[76]:   sid fcbb:bbbb:1:fe20::/64 locator MAIN behavior uDT6 vrf Vrf20
line 35: % Unknown command[76]:   sid fcbb:bbbb:1:fe30::/64 locator MAIN behavior uDT46 vrf Vrf30
line 41: % Unknown command[76]:   sid fcbb:bbbb:1:fe40::/64 locator MAIN behavior uA interface sr0 nexthop 2001::2
```

The problem is that in `frr-reload-py` all commands that start a new
multi-line context must be included in the `ctx_keyword` dictionary.
However, the `static-sids` command is not part of the `ctx_keyword`
dictionary.

This commit fixes the problem by adding `static-sids` to `ctx_keyword`.

Signed-off-by: Carmine Scarpitta <cscarpit@cisco.com>