pkg/report: parse "stack guard page was hit" better

Now that we increased CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT to 16
we started getting full parsable "stack guard page was hit" crashes.
Extract the anchor frame as we do for stalls.
This makes reports deterministic rather than point to a random top frame.

pkg/report/linux.go

@@ -1239,9 +1239,11 @@ var linuxOopses = append([]*oops{
 				stack: &stackFmt{
 					parts: []*regexp.Regexp{
 						linuxRipFrame,
+						linuxCallTrace,
+						parseStackTrace,
 					},
+					extractor: linuxStallFrameExtractor,
 				},
-				noStackTrace: true,
 			},
 			{
 				title: compile("BUG: Invalid wait context"),

pkg/report/testdata/linux/report/344

@@ -1,4 +1,5 @@
-TITLE: BUG: stack guard page was hit in __udp6_lib_lookup
+TITLE: BUG: stack guard page was hit in corrupted
+CORRUPTED: Y
 
 [  760.482711] BUG: stack guard page was hit at 00000000397c6d92 (stack is 00000000a0f6b86a..000000000e6f9570)
 [  760.492602] kernel stack overflow (double-fault): 0000 [#1] PREEMPT SMP