iovec-util: make IOVEC_TOTAL_SIZE() a regular function

The function isn't necessarily fast (it's O(n)), and there's no reason
to have it defined as inline function, since it's neither fast, nor
entirely trivial.

src/basic/iovec-util.c

@@ -3,6 +3,16 @@
 #include "iovec-util.h"
 #include "string-util.h"
 
+size_t iovec_total_size(const struct iovec *i, size_t n) {
+        size_t sum = 0;
+
+        assert(i || n == 0);
+
+        FOREACH_ARRAY(j, i, n)
+                sum += j->iov_len;
+
+        return sum;
+}
 
 char* set_iovec_string_field(struct iovec *iovec, size_t *n_iovec, const char *field, const char *value) {
         char *x;

src/basic/iovec-util.h

@@ -7,14 +7,7 @@
 
 #include "macro.h"
 
-static inline size_t IOVEC_TOTAL_SIZE(const struct iovec *i, size_t n) {
-        size_t r = 0;
-
-        for (size_t j = 0; j < n; j++)
-                r += i[j].iov_len;
-
-        return r;
-}
+size_t iovec_total_size(const struct iovec *i, size_t n);
 
 static inline bool IOVEC_INCREMENT(struct iovec *i, size_t n, size_t k) {
         /* Returns true if there is nothing else to send (bytes written cover all of the iovec),