ipsec, imsd, ims-pdn-up: the SA reader and the holds key compare in canonical form; LOCAL is canonicalised, PCSCF= accepted in RFC 5952 §4 form only

ParseExistingSa and SaLocals compared PCSCF= and LOCAL= as text against
`ip xfrm` output, which prints RFC 5952 form, so an upper-case or
uncompressed PCSCF= found no SAs and the restart registered fresh — on
KPN into the live-SA refusal; the holds file's pdn key compared the same
way. Both sides of each of those compares now go through
imsd::util::CanonicalAddr, LOCAL is canonicalised once on the way in, and PCSCF= is accepted in
that one spelling only — upper case, leading zeros or an uncompressed run
are refused at bring-up with the spelling to use, a dotted-quad tail (the
form ip prints for an IPv4-mapped address, which CanonicalIp6 does not read)
with the rule alone, a bracketed one by the bring-up script, which routes
the value as typed, with the rule (no brackets) — and a comma-separated
PCSCF= (a list) with its own message instead of reaching the socket layer: one spelling,
instead of a leniency both consumers of the setting would have to share.

Tested: crafter-build test, 7 passed; the upper-case PCSCF= refused with the spelling to use, a bracketed one
refused by the script, and the spelling they name resuming, in builds of
this series on the dev phone (KPN).

packaging/ims-pdn-up.sh

@@ -302,6 +302,7 @@ fi
 PCSCF=${PCSCF:-$(envval PCSCF)}
 case "$PCSCF" in
     '')  log "PCSCF not configured: no P-CSCF host route (imsd needs PCSCF= in /etc/imsd.env)" ;;
+    *\[*) log "PCSCF '$PCSCF': write the bare address, as ip prints it (no brackets)"; exit 1 ;;
     *:*) OUT=$(ip -6 route replace "$PCSCF/128" dev "$IFACE" 2>&1) ||
              { log "host route to P-CSCF $PCSCF failed: $(squash "$OUT")"; exit 1; }
          log "host route to P-CSCF $PCSCF dev $IFACE" ;;