sockets(examples): remove unused register, replace bzero with memset

• Remove the redundant register keyword from the variables, as most

compilers (GCC/Clang) just ignore them, and they're mostly just noise.

• Replace bzero() with memset(). IEEE 1003.1-2008 removes the spec of

bzero(), replacing it with memset().

• Use socklen_t (unsigned type) for variable b in the socket bind

example.

• Add unistd.h header file in the socket connect example (it is used by

the write() and read() libc calls). Remove unnecessary (char *) cast
from argv[1].

Signed-off-by: rilysh <nightquick@proton.me>
Reviewed-by: emaste@