Make sure to parse and load subprog exit/entry state information

[theihor]

Verifier prints subprog entry/exit state like this:

51: (85) call pc+705
caller:
 frame1: R6=2 R7=ctx() R8=map_value(map=map_xdp_setup,ks=4,vs=4) R9=pkt(r=0) R10=fp0 fp-336=????1
callee:
 frame2: R1=ctx() R2=scalar(smin=smin32=0,smax=umax=smax32=umax32=0xffff,var_off=(0x0; 0xffff)) R10=fp0

Currently bpfvv ignores these lines, and so does not record corresponding state change.

Sample log: https://lore.kernel.org/all/20250924151831.66c38c74@kernel.org/