gweb/gresolv: implement nameserver configuration for musl

I'm not able to test this on a system with glibc, however it works on Alpine/pmOS with musl (wifi was connected in this test, and it properly resolved the DNS over wan0 using my carrier's nameserver):

host ttnmmsget.msg.eng.t-mobile.com
flags 0
request /mms/wapenc?T=mavodi-7-13b-121-5-96-xxxxxx
lookup hostname ttnmmsget.msg.eng.t-mobile.com
g_resolv_lookup_hostname: nameserver_list NULL
Reading /etc/resolv.conf directly for nameservers
adding nameserver 192.168.1.1
addr = 100.198.113.108
setting nameserver 192.168.1.1
adding nameserver fd00:976a::9
fam 2 != expected 10
addr = 2607:fb90:806f:dfc8:997d:f5e2:a413:905a
setting nameserver fd00:976a::9
adding nameserver fd00:976a::10
fam 2 != expected 10
addr = 2607:fb90:806f:dfc8:997d:f5e2:a413:905a
setting nameserver fd00:976a::10
adding nameserver 10.177.0.34
addr = 100.198.113.108
setting nameserver 10.177.0.34
adding nameserver 10.177.0.210
addr = 100.198.113.108
setting nameserver 10.177.0.210
mmsd[15366]: ../src/service.c:get_messages()
mmsd[15366]: ../plugins/modemmanager.c:cb_get_sim_ready() Got SIM Path: /org/freedesktop/ModemManager1/SIM/0 Identifier: xxxxxxxx, imsi: xxxxxxxxx
response from fd00:976a::9
msg id: 0x6fd6 rcode: 0 count: 1
response from fd00:976a::10
msg id: 0x6fd6 rcode: 0 count: 1
response from fd00:976a::9
msg id: 0xcfb3 rcode: 0 count: 1
address 2607:7700:0:19:0:1:abc:4ba9
binding wwan0
no encryption
creating session 2607:7700:0:19:0:1:abc:4ba9:80
response from fd00:976a::10
msg id: 0xcfb3 rcode: 0 count: 1
request /mms/wapenc?T=mavodi-7-13b-121-5-96-xxxxxx from ttnmmsget.msg.eng.t-mobile.com
status 1 bytes to write 152 bytes written 152
bytes read 1368
[header] HTTP/1.1 200 OK