test: fix failing test-socket-util when running with ipv6.disable=1 kernel param The ability to use inet_pton(AF_INET6, ...) doesn't depend on kernel ipv6 support (inet_pton is a pure libc function), so make ipv6 address parsing tests unconditional.

util-lib: split out allocation calls into alloc-util.[ch]

util-lib: split out fd-related operations into fd-util.[ch] There are more than enough to deserve their own .c file, hence move them over.

util-lib: split our string related calls from util.[ch] into its own file string-util.[ch] There are more than enough calls doing string manipulations to deserve its own files, hence do something about it. This patch also sorts the #include blocks of all files that needed to be updated, according to the sorting suggestions from CODING_STYLE. Since pretty much every file needs our string manipulation functions this effectively means that most files have sorted #include blocks now. Also touches a few unrelated include files.

test-socket-util: add test for in_addr_is_null()

test-socket-util: add test for in_addr_to_string

treewide: no need to negate errno for log_*_errno() It corrrectly handles both positive and negative errno values.

treewide: auto-convert the simple cases to log_*_errno() As a followup to 086891e5c1 "log: add an "error" parameter to all low-level logging calls and intrdouce log_error_errno() as log calls that take error numbers", use sed to convert the simple cases to use the new macros: find . -name '*.[ch]' | xargs sed -r -i -e \ 's/log_(debug|info|notice|warning|error|emergency)\("(.*)%s"(.*), strerror\(-([a-zA-Z_]+)\)\);/log_\1_errno(-\4, "\2%m"\3);/' Multi-line log_*() invocations are not covered. And we also should add log_unit_*_errno().

test: only use assert_se The asserts used in the tests should never be allowed to be optimized away

tests: add tests for socket-util.c add tests for: - socket_address_is - socket_address_is_netlink - sockaddr_equal

test-socket-util: silence warnings

shared/socket-util: add function to query remote address

shared: split out in_addr related calls from socket-util.[ch] into its private in-addr-util.[ch] These are enough calls for a new file, and they are sufficiently different from the sockaddr-related calls, hence let's split this out.

networkd: add a number of calls to manipulate in_addr_union structs

tests: add test-socket-util