Crash when (wrongly) unapplying a policer

[jerome-labidurie]

A crash occurs in VPP when a policer is unapplied from an interface
with an index greater than the highest interface index to which a
policer has been applied.

Reproduction:

DBGvpp# create loopback interface 
loop0
DBGvpp# create loopback interface 
loop1
DBGvpp# policer add name p1 rate kbps cir 5000 cb 100000 conform-action transmit
DBGvpp# policer input unapply name p1 loop1
Code:  c7 04 88 ff ff ff ff 83 7d f0 00 75 28 8b 55 f4 8a 45 ef 24
#0  0x0000788c746e0248 policer_input + 0xc8
     from /lib/x86_64-linux-gnu/libvnet.so.25.06
#1  0x0000788c746e4a71 policer_input_command_fn + 0x251
     from /lib/x86_64-linux-gnu/libvnet.so.25.06
#2  0x0000788c7445cbe6 vlib_cli_dispatch_sub_commands + 0xd26
     from /lib/x86_64-linux-gnu/libvlib.so.25.06
#3  0x0000788c7445c9ae vlib_cli_dispatch_sub_commands + 0xaee
     from /lib/x86_64-linux-gnu/libvlib.so.25.06
#4  0x0000788c7445bcfa vlib_cli_input + 0x8a
     from /lib/x86_64-linux-gnu/libvlib.so.25.06
#5  0x0000788c744cc8b9 unix_cli_process_input + 0x519
     from /lib/x86_64-linux-gnu/libvlib.so.25.06
#6  0x0000788c744cab6b unix_cli_process + 0xab
     from /lib/x86_64-linux-gnu/libvlib.so.25.06
#7  0x0000788c744842ad vlib_process_bootstrap + 0x5d
     from /lib/x86_64-linux-gnu/libvlib.so.25.06
#8  0x0000788c7437d3c8
     from /lib/x86_64-linux-gnu/libvppinfra.so.25.06
Aborted (core dumped)

a fix is proposed here https://gerrit.fd.io/r/c/vpp/+/44843