bpf: Tidy up verifier check_func_arg()

bpf: Tidy up verifier check_func_arg()

This patch does two things:

1. For matching against the arg type, the match should be against the
base type of the arg type, since the arg type can have different
bpf_type_flags set on it.

2. Uses switch casing to improve readability + efficiency.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Acked-by: Hao Luo <haoluo@google.com>
Link: https://lore.kernel.org/r/20220712210603.123791-1-joannelkoong@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>