Fix fragment-offset-range pattern escaping in single-quoted strings

The pattern and posix-pattern for fragment-offset-range use '\\.'
(double backslash) in single-quoted YANG strings. Since single-quoted
strings have no escape processing (RFC 7950 Section 6.1.3), '\\.'
stores as literal backslash-backslash-dot, which in regex means
"literal backslash followed by any character" — not the intended
"literal dot".

All other patterns in the OpenConfig models correctly use '\.' (single
backslash) for literal dot matching in single-quoted strings (e.g.
area-address in openconfig-isis-types.yang).

Author: charanjith-anet

regexp-tests/openconfig-packet-match-types-test.yang

@@ -26,4 +26,23 @@ module openconfig-packet-match-types-test {
     pt:pattern-test-fail "66999..67890";
     pt:pattern-test-fail "70000..70000";
   }
+
+  leaf fragment-offset-range {
+    type oc-pkt-match-types:fragment-offset-range;
+    pt:pattern-test-pass "0..0";
+    pt:pattern-test-pass "0..8191";
+    pt:pattern-test-pass "8191..8191";
+    pt:pattern-test-pass "100..200";
+    pt:pattern-test-pass "00..00";
+    pt:pattern-test-pass "0000..0000";
+    pt:pattern-test-pass "1234..5678";
+    pt:pattern-test-pass "7999..8191";
+    pt:pattern-test-fail "100.200";
+    pt:pattern-test-fail "0.8191";
+    pt:pattern-test-fail "0..8192";
+    pt:pattern-test-fail "8192..8192";
+    pt:pattern-test-fail "9999..9999";
+    pt:pattern-test-fail "10000..10000";
+    pt:pattern-test-fail "-1..10";
+  }
 }

release/models/acl/openconfig-packet-match-types.yang

@@ -383,12 +383,12 @@ module openconfig-packet-match-types {
       type string {
         pattern
           '(0{0,3}[0-9]|0{0,2}[1-9][0-9]|0?[1-9][0-9]{2}|[1-7][0-9]{3}|'
-          + '80[0-9]{2}|81[0-8][0-9]|819[0-1])\\.\\.(0{0,3}[0-9]|'
+          + '80[0-9]{2}|81[0-8][0-9]|819[0-1])\.\.(0{0,3}[0-9]|'
           + '0{0,2}[1-9][0-9]|0?[1-9][0-9]{2}|[1-7][0-9]{3}|'
           + '80[0-9]{2}|81[0-8][0-9]|819[0-1])';
         oc-ext:posix-pattern
           '^((0{0,3}[0-9]|0{0,2}[1-9][0-9]|0?[1-9][0-9]{2}|[1-7][0-9]{3}|'
-          + '80[0-9]{2}|81[0-8][0-9]|819[0-1])\\.\\.(0{0,3}[0-9]|'
+          + '80[0-9]{2}|81[0-8][0-9]|819[0-1])\.\.(0{0,3}[0-9]|'
           + '0{0,2}[1-9][0-9]|0?[1-9][0-9]{2}|[1-7][0-9]{3}|'
           + '80[0-9]{2}|81[0-8][0-9]|819[0-1]))$';
       }