PC discontinuity reported as incorrect signal handler return point by invariant checker

Today we do not check PC discontinuities between an instr followed by a "kernel xfer" marker. If there is a discontinuity, it is reported as a "signal handler return point incorrect" invariant error later when the signal returns. E.g. the following

    28156078    20615075:       79758 ifetch       5 byte(s) @ 0x000000001a593862 66 45 89 0c fc       data16 mov    %r9w -> (%r12,%rdi,8)[2byte]
    28156079    20615075:       79758 write        2 byte(s) @ 0x0000177219ac0060 by PC 0x000000001a593862

// PC discontinuity in the kernel xfer marker address and prev instr. Not reported by invariant checker as such.
    28156080    20615075:       79758 <marker: kernel xfer from 0x1a59386d to handler>
...
    28156767    20615515:       79758 <marker: syscall xfer from 0x7ff30d21c1c9>

// Invariant error reported here due to mismatch with the pre_kernel_xfer instr (even though it is same as the kernel xfer marker address).
    28156770    20615516:       79758 ifetch       3 byte(s) @ 0x000000001a59386d 48 31 c0             xor    %rax %rax -> %rax

Such errors should be reported as what they are to avoid confusion.