tools, vtysh: fix ldpd + frr-reload.py

tools, vtysh: fix ldpd + frr-reload.py

frr-reload.py has many special case rules that did not consider ldpd
at all. Specifically:

 1. The bulk of ldp configuration comes in a big 'mpls ldp' context, which was
    previously considered a single-line context as it started with 'mpls'. This
    rule should only apply to labels and lsps.
 2. ldp has a 'router-id' config line that fell into the same rule as the above
    one. It should not be considered a single-line context as more ldp
    configuration can follow.
 3. enabled interfaces should not end their context. A better fix
    would actually require popping a new context for each interface
    in case there is any interface-specific config, but at least this
    fix will address the most common use case.
 4. when declaring pseudowires, any line with 'member pseudowire XXX' should
    be considered a sub-context of the 'l2vpn YYY type ZZZ' context. Without
    this fix, changes in the first psuedowire declared would not correctly
    be processed (e.g. removing a 'control-word exclude' line would not
    be picked up).

Signed-off-by: Emanuele Di Pascale <emanuele@voltanet.io>