tools: bpf: make use of reallocarray

tools: bpf: make use of reallocarray

reallocarray() is a safer variant of realloc which checks for
multiplication overflow in case of array allocation.  Since it's
not available in Glibc < 2.26 import kernel's overflow.h and
add a static inline implementation when needed.  Use feature
detection to probe for existence of reallocarray.

Signed-off-by: Jakub Kicinski <[email protected]>
Reviewed-by: Quentin Monnet <[email protected]>
Reviewed-by: Jiong Wang <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>