hostnamed: allow setting machine tags via udev rules (#42390)

This gives hostnamed a lot of love, and makes it possibly to "auto-tag"
a machine via a udev rule.

It builds on the machine tag concept added in v261.

src/basic/strv.c

@@ -812,16 +812,14 @@ bool strv_is_uniq(char * const *l) {
 }
 
 char** strv_remove(char **l, const char *s) {
-        char **f, **t;
-
         if (!l)
                 return NULL;
 
         assert(s);
 
-        /* Drops every occurrence of s in the string list, edits
-         * in-place. */
+        /* Drops every occurrence of s in the string list, edits in-place. */
 
+        char **f, **t;
         for (f = t = l; *f; f++)
                 if (streq(*f, s))
                         free(*f);
@@ -832,6 +830,17 @@ char** strv_remove(char **l, const char *s) {
         return l;
 }
 
+char** strv_remove_strv(char **l, char *const*ll) {
+
+        if (strv_isempty(l))
+                return l;
+
+        STRV_FOREACH(i, ll)
+                strv_remove(l, *i);
+
+        return l;
+}
+
 bool strv_overlap(char * const *a, char * const *b) {
         POINTER_MAY_BE_NULL(a);
         POINTER_MAY_BE_NULL(b);

src/basic/strv.h

@@ -85,6 +85,7 @@ int strv_consume_pair(char ***l, char *a, char *b);
 int strv_consume_prepend(char ***l, char *value);
 
 char** strv_remove(char **l, const char *s);
+char** strv_remove_strv(char **l, char *const*ll);
 char** strv_uniq(char **l);
 bool strv_is_uniq(char * const *l) _pure_;