Reland "adbd: don't close ep0 until we receive FUNCTIONFS_UNBIND."

Read until we receive FUNCTIONFS_BIND after every USB descriptor setup,
instead of only after initial creation of the control fd, so we properly
handle a rebind caused by a change of the USB configuration.

This reverts commit 55b31933f41b1c550b788fa2054010c51f56111b.

Bug: http://b/133132986
Bug: http://b/135155652
Test: manually enabled/disabled MTP with nonblocking_ffs enabled and disabled
Change-Id: Ibb3f46b8f84854ede47a669a85e07e16a5dd6008
Merged-In: Ibb3f46b8f84854ede47a669a85e07e16a5dd6008
(cherry picked from commit b00e66f7)