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).