create-diff-object: Fix out of range relocation verification check

[sumanthkorikkar]

kpatch_check_relocations() validates relocation targets using sec->data->d_size, which doesnt reflect entire section size.

Sections such as __bug_table may be represented by multiple records. In this case, data->d_size is lesser than the logical section size, leading to false out-of-range relocation errors.

ERROR: kernel/fork.o: kpatch_check_relocations:
.text.kernel_clone+0x2f6: out-of-range relocation __bug_table+0x1b2
sec_off: 432 sec_size: 48

The correct size of the section is sec->sh.sh_size, total size of __bug_table (480 bytes, corresponding to 30 struct bug_entry records).

Fix this by using sec->sh.sh_size instead of sec->data->d_size when verifying relocation bounds.

Additionally, ensure that newly rebuilt .kpatch.strings sections update sh.sh_size after the string table is finalized. Without this update, kpatch may fail with:

ERROR: kernel/fork.o: kpatch_check_relocations:
.kpatch.funcs+0x28: out-of-range relocation .kpatch.strings+0x8
sec_off: 8 sec_size: 0

[jpoimboe]

I think this is a side effect of trying to keep all the extra unneeded __bug_table entries. Instead I think the right fix is to not pull in the entire __bug_table, and instead adjust the .text.kernel_clone+0x2f6 reference to point to its bug table entry's new offset.