T8374: convert addresses to the host byte order before comparison in IPv4 range checks

[dmbaturin]

The original logic didn't account for the fact that in_addr->s_addr is stored in the network by order (big endian) and shouldn't be compared directly without byte order conversion on little-endian architectures.

That made certain checks like ipaddrcheck --verbose --is-ipv4-range 192.0.2.0-1.8.2.1 succeed, but the issue remained hidden because the comparison logic issue didn't affect more common bad ranges like 192.0.2.200-192.0.2.100.

In my defense, the POSIX docs for netinet/in.h doesn't say anything about the order and at the time I didn't realize the conversion happens much earlier than I thought.

Note that the IPv6 comparison logic is byte-by-byte from the start of the array, so it wasn't susceptible to that issue:

vyos_bld@75dc4f49e7e6:/vyos$ git diff
diff --git a/src/ipaddrcheck_functions.c b/src/ipaddrcheck_functions.c
index 09830a1..fa8351c 100644
--- a/src/ipaddrcheck_functions.c
+++ b/src/ipaddrcheck_functions.c
@@ -502,6 +502,7 @@ int compare_ipv6(struct in6_addr *left, struct in6_addr *right)
     int i = 0;
     for( i = 0; i < 16; i++ )
     {
+        printf("Comparing bytes %x and %x\n", left->s6_addr[i], right->s6_addr[i]);
         if (left->s6_addr[i] < right->s6_addr[i])
             return -1;
         else if (left->s6_addr[i] > right->s6_addr[i])

vyos_bld@75dc4f49e7e6:/vyos$ ./src/ipaddrcheck --is-ipv6-range aaaa:bbbb::1-aaaa:bbbb::10
Comparing bytes aa and aa
Comparing bytes aa and aa
Comparing bytes bb and bb
Comparing bytes bb and bb
Comparing bytes 0 and 0
Comparing bytes 0 and 0
Comparing bytes 0 and 0
Comparing bytes 0 and 0
Comparing bytes 0 and 0
Comparing bytes 0 and 0
Comparing bytes 0 and 0
Comparing bytes 0 and 0
Comparing bytes 0 and 0
Comparing bytes 0 and 0
Comparing bytes 0 and 0
Comparing bytes 1 and 10

Change Summary

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Other (please describe):

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• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[jestabro]

Fix obvious (in hindsight) bug; test added to confirm.